Merge branch 'master' of https://github.com/spulec/moto into 0.4.1-threadsafe

* 'master' of https://github.com/spulec/moto: (25 commits)
  Add @zkourouma to authors.
  0.4.2
  Fix bug where listener certificate was not being saved correctly when creating an elb. Added test to cover that case.
  [dynamodb2] adds lookup method to Table class
  Add IAM list_groups and list_groups_for_user. Closes #343.
  Fix for deleting Route53 record sets with set identifiers. Closes #342.
  Use dummy date instead of an invalid date
  Adding support for comments on hosted zones.
  Add availability zone support to Subnets created via CloudFormation
  Make availability zone dynamic in Subnet Response templates
  Add filter "availabilityZone" to DescribeSubnets and add availability zone support too
  allow starting without reseting
  Fix bug with empty string for instance vpc_id. Closes #337.
  Fix default security group description.
  Update responses.py
  Add @mrucci to authors.
  Fix merge conflicts.
  Add support for ELB attributes.
  cast to int when doing math.
  General cleanup.
  ...

moto/core/models.py

@@ -29,10 +29,11 @@ class MockAWS(object):
     def __exit__(self, *args):
         self.stop()
 
-    def start(self):
+    def start(self, reset=True):
         self.__class__.nested_count += 1
-        for backend in self.backends.values():
-            backend.reset()
+        if reset:
+            for backend in self.backends.values():
+                backend.reset()
 
         if not HTTPretty.is_enabled():
             HTTPretty.enable()