[shiftstack] Use GitHub for shiftstack-qa clone and fix false-positive test results

[imatza-rh]

Summary

Two fixes for the shiftstack CI role:

1. Clone shiftstack-qa from GitHub instead of GerritHub

shiftstack-qa moved code review to GitHub PRs (shiftstack/shiftstack-qa#2). The role default still clones from GerritHub, which is no longer maintained. GerritHub main is 3+ commits behind GitHub main - missing the 4-stable OCP channel switch, lb_tests disable, and .gitreview removal.

• Change cifmw_shiftstack_qa_repo default to https://github.com/shiftstack/shiftstack-qa
• Rename cifmw_shiftstack_qa_gerrithub_change to cifmw_shiftstack_qa_change_ref - supports both GitHub PR refs (refs/pull/N/head) and GerritHub change refs (refs/changes/...)

2. Fix false-positive test results in exec_command_in_pod.yml

In tp!2297 build d078ccbd, oc rsh returned rc=0 after 145s while the inner ansible-navigator playbook continued running in the pod for 21 minutes before failing. The shiftstack test reported PASS when OCP was never installed and zero Nova VMs were created. Verified on the live environment (serval70) - inner ansible-log.txt on the pod showed failed=1 at 10:59 UTC, but the outer oc rsh task had already completed with changed: [localhost] at 10:39 UTC.

The fix decouples the test result from the oc exec exit code:

• Writes the inner command exit code to a marker file on the pod (/tmp/cifmw_cmd_rc)
• Verifies the actual exit code in a separate oc exec call after the main command returns
• Polls with retries (up to 2h) to handle cases where the connection drops mid-execution
• Switches from oc rsh to oc exec for non-interactive pod commands

Test plan

• GitHub clone validated in tp!2297 build 70b1f455 (5h 8m) - OCP installed (51m), all cluster checks passed, only failed on Octavia LB (known OSPRH-29792)
• Exit code verification tested on live pod (serval70) - correctly catches false (exit 1) while passing echo hello (exit 0)
• YAML syntax validated
• Testproject re-validation with the exit code fix included

[openshift-ci]

Skipping CI for Draft Pull Request.
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[openshift-ci]

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