Added DE Background Scheduler w/ model sync jobs

In this changeset, I implemented a background scheduler service
for Watcher and more particularly for the Decision Engine where
I made it create 2 types of job per cluster data model collector
plugin:

- An initial job that is asynchronously executed upon starting the
  Decision Engine
- A periodical job that gets triggered every configurable interval
  of time

Change-Id: I3f5442f81933a19565217b894bd86c186e339762
Partially-Implements: bluprint cluster-model-objects-wrapper

watcher/tests/test_list_opts.py

@@ -29,10 +29,11 @@ class TestListOpts(base.TestCase):
             'api', 'watcher_decision_engine', 'watcher_applier',
             'watcher_planner', 'nova_client', 'glance_client',
             'cinder_client', 'ceilometer_client', 'neutron_client',
-            'watcher_clients_auth', 'watcher_planners.default']
+            'watcher_clients_auth']
+        self.opt_sections = list(dict(opts.list_opts()).keys())
 
     def test_run_list_opts(self):
-        expected_sections = self.base_sections
+        expected_sections = self.opt_sections
 
         result = opts.list_opts()