Only check if MongoDB is running once durring tests

This should increase the speed of the unit test process because
it changes the check for if MongoDB is running from every time
a test case is run, to only once per test case.

tests/base_case.py

@@ -42,7 +42,8 @@ def tearDown(self):
 
 class ChatBotMongoTestCase(ChatBotTestCase):
 
- def setUp(self):
+ @classmethod
+ def setUpClass(cls):
  from pymongo.errors import ServerSelectionTimeoutError
  from pymongo import MongoClient
 
@@ -56,8 +57,6 @@ def setUp(self):
  except ServerSelectionTimeoutError:
  raise SkipTest('Unable to connect to Mongo DB.')
 
- super(ChatBotMongoTestCase, self).setUp()
-
  def get_kwargs(self):
  kwargs = super(ChatBotMongoTestCase, self).get_kwargs()
  kwargs['database'] = self.random_string()