Build and maintain Gerrit support.
- Piotr Sikora
- GerritStatusPush: missing retrying mechanism for status updates
- GerritChangeSource should ignore incoming ref-updated events to refs/meta/config branch
- GerritChangeFilter support for branch filtering is broken
- GerritChangeFilter doesn't trigger a builder if a push is done without a gerrit review
- gerritStartCB don't work