Use tags instead of branches for release candidates.
Use tags instead of branches for release candidates.

Reviewed at https://reviews.apache.org/r/42145/

medallia/aurora,crashlytics/aurora,protochron/aurora,medallia/aurora,rdelval/aurora,crashlytics/aurora,protochron/aurora,thinker0/aurora,rdelval/aurora,thinker0/aurora,protochron/aurora,apache/aurora,thinker0/aurora,thinker0/aurora,rdelval/aurora,apache/aurora,thinker0/aurora,crashlytics/aurora,apache/aurora,apache/aurora,crashlytics/aurora,rdelval/aurora,rdelval/aurora,apache/aurora,medallia/aurora,protochron/aurora,thinker0/aurora,crashlytics/aurora,medallia/aurora,rdelval/aurora,protochron/aurora,crashlytics/aurora,protochron/aurora,medallia/aurora,apache/aurora,medallia/aurora