Change beaker session backend to database

A memory backend isn't as suitable for production.
Switching the backend to database to see if we
can resolve from session issues we are having on
refstack.openstack.org. This will also allow sessions to
persist across apache restarts.

Change-Id: Iaf98d1f50adc5667a8e3a878b9c91fc9d65eb419

refstack/api/app.py

@@ -213,7 +213,8 @@ def setup_app(config):
 
     beaker_conf = {
         'session.key': 'refstack',
-        'session.type': 'memory',
+        'session.type': 'ext:database',
+        'session.url': CONF.database.connection,
         'session.timeout': 604800,
         'session.validate_key': api_utils.get_token(),
     }

refstack/tests/unit/test_app.py

@@ -196,6 +196,9 @@ class SetupAppTestCase(base.BaseTestCase):
         self.CONF.set_override('static_root',
                                'fake_static_root',
                                'api')
+        self.CONF.set_override('connection',
+                               'fake_connection',
+                               'database')
 
         os_join.return_value = 'fake_project_root'
 
@@ -222,7 +225,8 @@ class SetupAppTestCase(base.BaseTestCase):
         session_middleware.assert_called_once_with(
             'fake_app',
             {'session.key': 'refstack',
-             'session.type': 'memory',
+             'session.type': 'ext:database',
+             'session.url': 'fake_connection',
              'session.timeout': 604800,
              'session.validate_key': get_token.return_value}
         )