Update Gerrit Trigger keywords to be specific

In global-jjb the adopted best practice for trigger keywords is to be precise. Rather than checking for the keyword anywhere in the comment check for exactly that comment when possible. This is to prevent jobs from triggering accidentally when folks where using the keyword in a sentence.

releng/builder should be updated to follow this format for consistency as some folks leave trailing comments in their comment triggers. This would cause some jobs to spawn but not others and is a case for confusion.