Allow to retrigger outdated pipelines

Sometimes, the merge job git ref validation for retriggered pipelines fails because a newer version of the feature branch is already available, but has no green pipeline that could get picked up by the bot.

Be a bit more forgiving in this case by allowing to use the same git commit as in the original pipeline if that one ran as a merged result pipeline and therefore the merge commit is known.

Part of the validation for containers#45 (closed)

Signed-off-by: Michael Hofmann mhofmann@redhat.com