zuul: bring in geard stats

The Zuul gearman embeded server now reports statistics!

Change-Id: I6359eafbea00d33a88bc7e34dd31a6f9ecc623ed
zuul: drop Gerrit events graphs (broken)

The Gerrit events are broken in statsd so there is no point in keeping
the graph around for now.

Change-Id: I834b270575e571e3fee4d11b9b08c378fe8f2d7f