don't pass aodh options to oslo.db engine facade

oslo.db EngineFacade class only support options defined by oslo.db,
but we also pass options defined by aodh, so oslo.db complains
with a warning message:

NotSupportedWarning: Configuration option(s) ['alarm_connection', \
'alarm_history_time_to_live'] not supported

This patch makes sure only options defined by oslo.db will be sent
to EngineFacade

Change-Id: I4c259f29af1cab60c3aee41a610b12f64ed5f2d5
Closes-Bug: #1516515

aodh/storage/impl_sqlalchemy.py

@@ -26,6 +26,7 @@ import six
 from sqlalchemy import desc
 
 from aodh.i18n import _LI
+from aodh import storage
 from aodh.storage import base
 from aodh.storage import models as alarm_api_models
 from aodh.storage.sqlalchemy import models
@@ -63,8 +64,11 @@ class Connection(base.Connection):
         # in storage.__init__.get_connection_from_config function
         options = dict(conf.database.items())
         options['max_retries'] = 0
-        self.conf = conf
+        # oslo.db doesn't support options defined by Aodh
+        for opt in storage.OPTS:
+            options.pop(opt.name, None)
         self._engine_facade = db_session.EngineFacade(url, **options)
+        self.conf = conf
 
     def disconnect(self):
         self._engine_facade.get_engine().dispose()