Refactor metric collection

This change adds a generic queue onto which metrics can be pushed. A
separate module removes metrics from the queue and adds them to Cloudwatch.
Since these are now separate ideas, we can easily change the consumer from
Cloudwatch to anything else.

This change maintains near feature parity (the only change is there is now
just one queue instead of two - not a big deal).

buildman/server.py

@@ -16,7 +16,7 @@ from buildman.enums import BuildJobResult, BuildServerStatus
 from buildman.jobutil.buildstatus import StatusHandler
 from buildman.jobutil.buildjob import BuildJob, BuildJobLoadException
 from data import database
-from app import app, build_metrics
+from app import app, metric_queue
 
 logger = logging.getLogger(__name__)
 
@@ -151,7 +151,7 @@ class BuilderServer(object):
     if self._current_status == BuildServerStatus.SHUTDOWN and not self._job_count:
       self._shutdown_event.set()
 
-    build_metrics.report_completion_status(job_status)
+    report_completion_status(job_status)
 
   @trollius.coroutine
   def _work_checker(self):
@@ -225,3 +225,15 @@ class BuilderServer(object):
 
     # Initialize the work queue checker.
     yield From(self._work_checker())
+
+def report_completion_status(status):
+  if status == BuildJobResult.COMPLETE:
+    status_name = 'CompleteBuilds'
+  elif status == BuildJobResult.ERROR:
+    status_name = 'FailedBuilds'
+  elif status == BuildJobResult.INCOMPLETE:
+    status_name = 'IncompletedBuilds'
+  else:
+    return
+
+  metric_queue.put(status_name, 1, unit='Count')