Implemented GMR plugin to show CDM structures

In this changeset, I implemented a small GMR plugin that converts
the cluster data model structure into an XML structure.

Change-Id: I75548952635a0aa3c7dbd6d068831b5765a5db1a
Closes-Bug: #1620551

watcher/cmd/decisionengine.py

@@ -25,6 +25,7 @@ from oslo_log import log as logging
 
 from watcher._i18n import _LI
 from watcher.common import service as watcher_service
+from watcher.decision_engine import gmr
 from watcher.decision_engine import manager
 from watcher.decision_engine import scheduling
 from watcher.decision_engine import sync
@@ -35,6 +36,7 @@ CONF = cfg.CONF
 
 def main():
     watcher_service.prepare_service(sys.argv)
+    gmr.register_gmr_plugins()
 
     LOG.info(_LI('Starting Watcher Decision Engine service in PID %s'),
              os.getpid())