Allow for dropping of the default retention policy

This no longer raises an error and simply results in no retention policy being set for the database.

Author: wwentland

influxdb/tests/server_tests/client_test_with_server.py

@@ -604,16 +604,6 @@ def test_drop_retention_policy(self):
  rsp
  )
 
- def test_drop_retention_policy_default(self):
- # Test drop default retention
- with self.assertRaises(InfluxDBClientError) as ctx:
- self.cli.drop_retention_policy('default', 'db')
-
- self.assertEqual(400, ctx.exception.code)
- self.assertIn(
- '{"error":"error parsing query: found DEFAULT, expected POLICY',
- ctx.exception.content)
-
  def test_issue_143(self):
  pt = partial(point, 'a_serie_name', timestamp='2015-03-30T16:16:37Z')
  pts = [