Add PolyGerrit validation for merge commits
Add PolyGerrit validation for merge commits

Change-Id: I4356aa84d316ec730ba158776aebe06d45db6cec

GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit