Add cluster subnet group CRUD.

moto/ec2/models.py

@@ -1576,6 +1576,12 @@ class Subnet(TaggedEC2Resource):
         )
         return subnet
 
+    @property
+    def availability_zone(self):
+        # This could probably be smarter, but there doesn't appear to be a
+        # way to pull AZs for a region in boto
+        return self.ec2_backend.region_name + "a"
+
     @property
     def physical_resource_id(self):
         return self.id
@@ -2435,6 +2441,15 @@ class EC2Backend(BaseBackend, InstanceBackend, TagBackend, AmiBackend,
                  ElasticAddressBackend, KeyPairBackend, DHCPOptionsSetBackend,
                  NetworkAclBackend):
 
+    def __init__(self, region_name):
+        super(EC2Backend, self).__init__()
+        self.region_name = region_name
+
+    def reset(self):
+        region_name = self.region_name
+        self.__dict__ = {}
+        self.__init__(region_name)
+
     # Use this to generate a proper error template response when in a response handler.
     def raise_error(self, code, message):
         raise EC2ClientError(code, message)
@@ -2488,4 +2503,4 @@ class EC2Backend(BaseBackend, InstanceBackend, TagBackend, AmiBackend,
 
 ec2_backends = {}
 for region in boto.ec2.regions():
-    ec2_backends[region.name] = EC2Backend()
+    ec2_backends[region.name] = EC2Backend(region.name)