Enhance the db layer to verify filters

Now if we init filters=None, as call
dbapi.device_profile_list_by_filters(self.context, filters=None),
that will raise an NoneType error.

Mainly error info:
Traceback (most recent call last):
  File "/home/my_work/code/cyborg/cyborg/db/sqlalchemy/api.py", line
558, in device_profile_list_by_filters
    filters, exact_match_filter_names)
  File "/home/my_work/code/cyborg/cyborg/db/sqlalchemy/api.py", line
223, in _exact_filter
    if key not in filters:
TypeError: argument of type 'NoneType' is not iterable

This patch will add initial validation of the filters.

Change-Id: Icf711dc3621fb8d2e5b022ab1d1ce02b0885b055

cyborg/db/sqlalchemy/api.py

@@ -211,6 +211,8 @@ class Connection(api.Connection):
         :param legal_keys: list of keys to apply exact filtering to
         """
 
+        if filters is None:
+            filters = {}
         if legal_keys is None:
             legal_keys = []
         filter_dict = {}

cyborg/tests/unit/db/test_db_device_profile.py

@@ -86,6 +86,21 @@ class TestDbDeviceProfile(base.DbTestCase):
                           self.dbapi.device_profile_get_by_uuid,
                           self.context, random_uuid)
 
+    def test_list_filter_is_none(self):
+        """The main test is filters=None. If filters=None,
+        it will be initialized to {}, that will return all device
+        profiles same as the List Device Profiles API response.
+        """
+        utils.create_test_device_profile(
+            self.context,
+            id=1,
+            uuid=uuidutils.generate_uuid(),
+            name="foo_dp")
+        res = self.dbapi.device_profile_list_by_filters(
+            self.context, filters=None)
+        self.assertEqual(1, len(res))
+        self.assertEqual('foo_dp', res[0]['name'])
+
     def test_update_with_uuid_not_exist(self):
         utils.create_test_device_profile(self.context)
         random_uuid = uuidutils.generate_uuid()