CIT: Support SSH connections to hosts that block SHA1

[EricEdens]

The SSH tests in CIT use Go to establish SSH connections:

guest-test-infra/imagetest/utils/test_utils.go

Line 192 in 99181c4

func CreateClient(user, host string, pembytes []byte) (*ssh.Client, error) {

While running CIT against Ubuntu 22.04, I observed that the SSH tests were failing:

	<testsuite name="ssh-daily-ubuntu-2204-jammy-v20220415" tests="5" failures="2" errors="0" disabled="0" skipped="0" time="0">
		<testcase classname="ssh-daily-ubuntu-2204-jammy-v20220415" name="TestMatchingKeysInGuestAttributes" time="0.02"></testcase>
		<testcase classname="ssh-daily-ubuntu-2204-jammy-v20220415" name="TestHostKeysAreUnique" time="60.2">
			<failure type="">    host_key_test.go:59: connect to remote host at 1650057165249076651&#xA;    host_key_test.go:62: user test-user failed ssh to target host, vm2-ssh-3jtbh, err ssh: handshake failed: ssh: unable to authenticate, attempted methods [none publickey], no supported methods remain</failure>
		</testcase>
		<testcase classname="ssh-daily-ubuntu-2204-jammy-v20220415" name="TestSSHInstanceKey" time="60.14">
			<failure type="">    image_ssh_test.go:33: connect to remote host at 1650057225390562509&#xA;    image_ssh_test.go:36: user test-user failed ssh to target host, vm2-ssh-3jtbh, err ssh: handshake failed: ssh: unable to authenticate, attempted methods [none publickey], no supported methods remain</failure>
		</testcase>
		<testcase classname="ssh-daily-ubuntu-2204-jammy-v20220415" name="TestEmptyTest" time="0"></testcase>
		<testcase classname="ssh-daily-ubuntu-2204-jammy-v20220415" name="TestHostKeysNotOverrideAfterAgentRestart" time="0.12"></testcase>
	</testsuite>

This occurred since Ubuntu 22.04 updated to an OpenSSH version that blocks connections that use SHA-1: https://www.openssh.com/releasenotes.html

This PR updates the golang.org/x/crypto dependency, which brings in their PR to support SHA-2 keys: golang/go#37278

It also does the following:

• Creates a go.mod file in the imagetest directory
• Updates the container build configurations to build relative to this directory

[hopkiw]

/hold

so the main issue here is we need to confirm changing the shared go.mod doesn't break any of the containers, and if it does, we'll have to create per-project go modules either for the old or the new

[EricEdens]

so the main issue here is we need to confirm changing the shared go.mod doesn't break any of the containers, and if it does, we'll have to create per-project go modules either for the old or the new

@hopkiw

This PR creates a new go.mod and leaves the old one unchanged. :)

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: EricEdens, hopkiw

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[hopkiw]

/unhold