Enable Gerrit httpd requestLog

Because we proxy to Gerrit and set listenUrl with a proxy-http:// prefix
httpd.requestLog is disabled by default. We choose to explicitly enable
it here to add more logging to the Gerrit system even if this logging is
slightly less useful when behind a proxy. In particular this logging
will track memory utilization per request which we can use to benchmark
change query memory cost between 3.4 and 3.5.

Change-Id: Ia3ccf820ee0e5ca7d68bcc37da7004dea2ad7128

playbooks/roles/gerrit/templates/gerrit.config.j2

@@ -55,6 +55,7 @@
 	minThreads = 20
 	maxThreads = 100
 	maxQueued = 200
+	requestLog = true
 [cache]
 	directory = cache
 [cache "accounts"]