Bug Fix: Parses notifier configuration options

Successfully parses configuration options for enabled notifiers.
IMPORTANT: This requires the built-in notifiers be "enabled"
in the configuration.

This patch is compliant with `https://review.openstack.org/#/c/435136/`
that in summary makes every notifier pluggable as apposed distinguished
built-in and pluggable notifiers.

Change-Id: I818212344268de5e90e72c5493a8632476ba254b
Story: #2003794
Task: #26507

monasca_notification/conf/__init__.py

@@ -54,6 +54,14 @@ def register_opts(conf=None):
         m.register_opts(conf)
 
 
+def register_enabled_plugin_opts(conf=None):
+    if conf is None:
+        conf = CONF
+    for enabled_plugin in conf.notification_types.enabled:
+        ep_module = importutils.import_module(".".join(enabled_plugin.split(".")[:-1]))
+        ep_module.register_opts(conf)
+
+
 def list_opts():
     opts = collections.defaultdict(list)
     for m in CONF_OPTS:

monasca_notification/config.py

@@ -45,6 +45,9 @@ def parse_args(argv, no_yaml=False):
          monasca-notification is an engine responsible for
          transforming alarm transitions into proper notifications
          ''')
+
+    conf.register_enabled_plugin_opts(CONF)
+
     log.setup(CONF,
               product_name='monasca-notification',
               version=version.version_string)