Add gear statsd support

Gear 0.5.0 added statsd support for the gear server.  Have Zuul
use it based on the existence of the same env vars Zuul uses
to configure its own use of statsd.

Change-Id: I09ea2541d1f2eff5f4fd2e0c78da2acfdc1776ab

zuul/cmd/server.py

@@ -154,7 +154,13 @@ class Server(object):
             os.close(pipe_write)
             self.setup_logging('gearman_server', 'log_config')
             import gear
-            gear.Server(4730)
+            statsd_host = os.environ.get('STATSD_HOST')
+            statsd_port = int(os.environ.get('STATSD_PORT', 8125))
+            gear.Server(4730,
+                        statsd_host=statsd_host,
+                        statsd_port=statsd_port,
+                        statsd_prefix='zuul.geard')
+
             # Keep running until the parent dies:
             pipe_read = os.fdopen(pipe_read)
             pipe_read.read()