Update gerrit comment trigger keywords with regex

Update gerrit comment trigger keywords with regex

Update gerrit comment trigger to use standard regex
and avoid triggering jobs, when these keywords are used as
gerrit comments between users.

Change-Id: Iac67e9508fd600650c4ed351094cfdaf2e212835
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>