multitenant: \demo add is broken in multi-tenant mode

[ajstorm]

Describe the problem

The \demo add statement which adds nodes to a demo cluster is broken when demo runs in multi-tenant mode.

To Reproduce

• cockroach demo --nodes 9
• \demo add "region=us-central1"
• \demo ls

Application tenant:
*
* ERROR: a panic has occurred!
* runtime error: index out of range [9] with length 9
* (1) attached stack trace
*   -- stack trace:
*   | runtime.gopanic
*   | 	GOROOT/src/runtime/panic.go:890
*   | runtime.goPanicIndex
*   | 	GOROOT/src/runtime/panic.go:113
*   | github.com/cockroachdb/cockroach/pkg/cli/democluster.(*transientCluster).ListDemoNodes
*   | 	github.com/cockroachdb/cockroach/pkg/cli/democluster/demo_cluster.go:1902
*   | github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).handleDemo
*   | 	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:696
*   | github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).doHandleCliCmd
*   | 	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:1579
*   | github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).doRunShell
*   | 	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:2326
*   | github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).RunInteractive
*   | 	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:2275
*   | github.com/cockroachdb/cockroach/pkg/cli/clisqlcfg.(*Context).Run
*   | 	github.com/cockroachdb/cockroach/pkg/cli/clisqlcfg/context.go:225
*   | github.com/cockroachdb/cockroach/pkg/cli.runDemoInternal
*   | 	github.com/cockroachdb/cockroach/pkg/cli/demo.go:383
*   | github.com/cockroachdb/cockroach/pkg/cli.runDemo
*   | 	github.com/cockroachdb/cockroach/pkg/cli/demo.go:200
*   | github.com/cockroachdb/cockroach/pkg/cli.init.5.func1
*   | 	github.com/cockroachdb/cockroach/pkg/cli/demo.go:59
*   | github.com/cockroachdb/cockroach/pkg/cli/clierrorplus.MaybeDecorateError.func1
*   | 	github.com/cockroachdb/cockroach/pkg/cli/clierrorplus/decorate_error.go:72
*   | github.com/spf13/cobra.(*Command).execute
*   | 	github.com/spf13/cobra/external/com_github_spf13_cobra/command.go:856
*   | github.com/spf13/cobra.(*Command).ExecuteC
*   | 	github.com/spf13/cobra/external/com_github_spf13_cobra/command.go:974
*   | github.com/spf13/cobra.(*Command).Execute
*   | 	github.com/spf13/cobra/external/com_github_spf13_cobra/command.go:902
*   | github.com/cockroachdb/cockroach/pkg/cli.Run
*   | 	github.com/cockroachdb/cockroach/pkg/cli/cli.go:300
*   | github.com/cockroachdb/cockroach/pkg/cli.doMain
*   | 	github.com/cockroachdb/cockroach/pkg/cli/cli.go:143
*   | github.com/cockroachdb/cockroach/pkg/cli.Main
*   | 	github.com/cockroachdb/cockroach/pkg/cli/cli.go:68
*   | main.main
*   | 	main/pkg/cmd/cockroach/main.go:26
*   | runtime.main
*   | 	GOROOT/src/runtime/proc.go:250
*   | runtime.goexit
*   | 	GOROOT/src/runtime/asm_arm64.s:1172
* Wraps: (2) runtime error: index out of range [9] with length 9
* Error types: (1) *withstack.withStack (2) runtime.boundsError
*
panic: runtime error: index out of range [9] with length 9 [recovered]
	panic: runtime error: index out of range [9] with length 9 [recovered]
	panic: runtime error: index out of range [9] with length 9

goroutine 1 [running]:
github.com/cockroachdb/cockroach/pkg/util/log/logcrash.RecoverAndReportPanic({0x109ab68c0, 0x140001a8010}, 0x140283e8c88?)
	github.com/cockroachdb/cockroach/pkg/util/log/logcrash/crash_reporting.go:132 +0x74
panic({0x1096a9820, 0x1403f187248})
	GOROOT/src/runtime/panic.go:884 +0x204
github.com/cockroachdb/cockroach/pkg/cli/democluster.(*transientCluster).Close(0x14002f20000, {0x109ab68c0?, 0x140001a8010})
	github.com/cockroachdb/cockroach/pkg/cli/democluster/demo_cluster.go:968 +0x1cc
panic({0x1096a9820, 0x1403f187248})
	GOROOT/src/runtime/panic.go:890 +0x258
github.com/cockroachdb/cockroach/pkg/cli/democluster.(*transientCluster).ListDemoNodes(0x14002f20000, {0x109a70aa0, 0x140001c0008}, {0x109a70aa0, 0x140005aa060}, 0x0, 0x1)
	github.com/cockroachdb/cockroach/pkg/cli/democluster/demo_cluster.go:1902 +0x9d8
github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).handleDemo(0x1401befe940?, {0x14024234050?, 0x10748a028?, 0x1?}, 0x140627271f8?, 0x0?)
	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:696 +0x84
github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).doHandleCliCmd(0x1401cbd1b80, 0x2, 0x14028f29308?)
	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:1579 +0xa50
github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).doRunShell(0x1401cbd1b80, 0x119ac5cb8?, 0x10f8bcf18?, 0xd0?, 0x140005aa060)
	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:2326 +0x2fc
github.com/cockroachdb/cockroach/pkg/cli/clisqlshell.(*cliState).RunInteractive(0x14000e431d0?, 0x109b25260?, 0x14011ecf520?, 0x140130b0870?)
	github.com/cockroachdb/cockroach/pkg/cli/clisqlshell/sql.go:2275 +0x5c
github.com/cockroachdb/cockroach/pkg/cli/clisqlcfg.(*Context).Run(0x14000e431d0, {0x109ab68c0, 0x140001a8010}, {0x109b25260?, 0x14011ecf520})
	github.com/cockroachdb/cockroach/pkg/cli/clisqlcfg/context.go:225 +0x2ec
github.com/cockroachdb/cockroach/pkg/cli.runDemoInternal(0x10dab3020, {0x0, 0x0}, 0x109a08a80)
	github.com/cockroachdb/cockroach/pkg/cli/demo.go:383 +0xc40
github.com/cockroachdb/cockroach/pkg/cli.runDemo(...)
	github.com/cockroachdb/cockroach/pkg/cli/demo.go:200
github.com/cockroachdb/cockroach/pkg/cli.init.5.func1(0x9?, {0x1400099da38?, 0x1?, 0xc?})
	github.com/cockroachdb/cockroach/pkg/cli/demo.go:59 +0x2c
github.com/cockroachdb/cockroach/pkg/cli/clierrorplus.MaybeDecorateError.func1(0x10dab3020?, {0x1400129e1e0?, 0x2?, 0x2?})
	github.com/cockroachdb/cockroach/pkg/cli/clierrorplus/decorate_error.go:72 +0x34
github.com/spf13/cobra.(*Command).execute(0x10dab3020, {0x1400129e1c0, 0x2, 0x2})
	github.com/spf13/cobra/external/com_github_spf13_cobra/command.go:856 +0x4dc
github.com/spf13/cobra.(*Command).ExecuteC(0x10daab0a0)
	github.com/spf13/cobra/external/com_github_spf13_cobra/command.go:974 +0x360
github.com/spf13/cobra.(*Command).Execute(...)
	github.com/spf13/cobra/external/com_github_spf13_cobra/command.go:902
github.com/cockroachdb/cockroach/pkg/cli.Run(...)
	github.com/cockroachdb/cockroach/pkg/cli/cli.go:300
github.com/cockroachdb/cockroach/pkg/cli.doMain(0x10dab3020, {0x1400340401a, 0x4})
	github.com/cockroachdb/cockroach/pkg/cli/cli.go:143 +0x1cc
github.com/cockroachdb/cockroach/pkg/cli.Main()
	github.com/cockroachdb/cockroach/pkg/cli/cli.go:68 +0x194
main.main()
	main/pkg/cmd/cockroach/main.go:26 +0x1c

Expected behavior
No panic. Lists all nodes (including the newly added 10th node)

Jira issue: CRDB-30244
Epic: CRDB-26691