Fix flaky kubeexec unit test case with env vars

[rm3l]

What type of PR is this:
/kind tests
/area testing

What does this PR do / why we need it:
Unit tests in pkg/remotecmd/kubeexec_test.go expect an exact command-line string to be passed when running commands in containers. The problem is that the environment variables are stored in a map, the iteration order of which is not guaranteed.

Initially reported in #5823 (comment)

Which issue(s) this PR fixes:

==================
--- FAIL: TestKubeExecProcessHandler_StartProcessForCommand (10.00s)
    --- FAIL: TestKubeExecProcessHandler_StartProcessForCommand/command_with_all_fields_returned_no_error (10.00s)
        remotecmd.go:36: Unexpected call to *kclient.MockClientInterface.ExecCMDInContainer([my-container my-pod [/bin/sh -c echo $$ > /opt/odo/.odo_devfile_cmd_my-exec-cmd.pid && cd /path/to/working/dir && export ENV_VAR2='value2' ENV_VAR1='value1' && (tail -f /path/to/a/file) 1>>/proc/1/fd/1 2>>/proc/1/fd/2] 0xc00047a030 0xc00047a040 <nil> false]) at /workspace/dcb6538f-a4d0-4109-85f2-86d8f7960de8/pkg/remotecmd/remotecmd.go:36 because: 
            expected call at /workspace/dcb6538f-a4d0-4109-85f2-86d8f7960de8/pkg/remotecmd/kubexec_test.go:185 doesn't match the argument at index 2.
            Got: [/bin/sh -c echo $$ > /opt/odo/.odo_devfile_cmd_my-exec-cmd.pid && cd /path/to/working/dir && export ENV_VAR2='value2' ENV_VAR1='value1' && (tail -f /path/to/a/file) 1>>/proc/1/fd/1 2>>/proc/1/fd/2]
            Want: is equal to [/bin/sh -c echo $$ > /opt/odo/.odo_devfile_cmd_my-exec-cmd.pid && cd /path/to/working/dir && export ENV_VAR1='value1' ENV_VAR2='value2' && (tail -f /path/to/a/file) 1>>/proc/1/fd/1 2>>/proc/1/fd/2]
        kubexec_test.go:219: timeout waiting for output handler to get called
        controller.go:137: missing call(s) to *kclient.MockClientInterface.ExecCMDInContainer(is equal to my-container, is equal to my-pod, is equal to [/bin/sh -c echo $$ > /opt/odo/.odo_devfile_cmd_my-exec-cmd.pid && cd /path/to/working/dir && export ENV_VAR1='value1' ENV_VAR2='value2' && (tail -f /path/to/a/file) 1>>/proc/1/fd/1 2>>/proc/1/fd/2], is anything, is anything, is anything, is anything) /workspace/dcb6538f-a4d0-4109-85f2-86d8f7960de8/pkg/remotecmd/kubexec_test.go:185
        controller.go:137: aborting test due to missing call(s)
        testing.go:1092: race detected during execution of test
    testing.go:1092: race detected during execution of test
FAIL
FAIL	[github.com/redhat-developer/odo/pkg/remotecmd](http://github.com/redhat-developer/odo/pkg/remotecmd)	16.453s

PR acceptance criteria:

• Unit test

• Integration test

• Documentation

How to test changes / Special notes to the reviewer:
All tests in kubeexec_test.go should pass.

cc @feloy

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[feloy]

/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: feloy

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[feloy]

Thanks @rm3l for the quick fix

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[feloy]

/lgtm

[feloy]

/override ci/prow/v4.10-integration-e2e

[openshift-ci]

@feloy: Overrode contexts on behalf of feloy: ci/prow/v4.10-integration-e2e

In response to this:

/override ci/prow/v4.10-integration-e2e

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