Fix #1830 Add support for cross-region VPC peering

Add a class level store in models/VPCBackend of ec2
for saving vpcs of all regions info. Any instance can correctly find vpc in another region
when connecting vpc of cross-region or vpc of same region.

Modify vpc_peering_connections in ec2/responses to handle
vpc peering of same region or cross region.

Update vpc_peering_connections response
template content to latest (2016-11-15) .

Add vpc cross region peering successful test case.
Add vpc cross region peering fail test case.

Related: https://github.com/spulec/moto/issues/1830

Reference
CreateVpcPeeringConnection Sample Response
https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CreateVpcPeeringConnection.html

moto/ec2/models.py

@@ -13,6 +13,7 @@ from pkg_resources import resource_filename
 import boto.ec2
 
 from collections import defaultdict
+import weakref
 from datetime import datetime
 from boto.ec2.instance import Instance as BotoInstance, Reservation
 from boto.ec2.blockdevicemapping import BlockDeviceMapping, BlockDeviceType
@@ -2115,10 +2116,20 @@ class VPC(TaggedEC2Resource):
 
 
 class VPCBackend(object):
+    __refs__ = defaultdict(list)
+
     def __init__(self):
         self.vpcs = {}
+        self.__refs__[self.__class__].append(weakref.ref(self))
         super(VPCBackend, self).__init__()
 
+    @classmethod
+    def get_instances(cls):
+        for inst_ref in cls.__refs__[cls]:
+            inst = inst_ref()
+            if inst is not None:
+                yield inst
+
     def create_vpc(self, cidr_block, instance_tenancy='default', amazon_provided_ipv6_cidr_block=False):
         vpc_id = random_vpc_id()
         vpc = VPC(self, vpc_id, cidr_block, len(self.vpcs) == 0, instance_tenancy, amazon_provided_ipv6_cidr_block)
@@ -2142,6 +2153,13 @@ class VPCBackend(object):
             raise InvalidVPCIdError(vpc_id)
         return self.vpcs.get(vpc_id)
 
+    # get vpc by vpc id and aws region
+    def get_cross_vpc(self, vpc_id, peer_region):
+        for vpcs in self.get_instances():
+            if vpcs.region_name == peer_region:
+                match_vpc = vpcs.get_vpc(vpc_id)
+        return match_vpc
+
     def get_all_vpcs(self, vpc_ids=None, filters=None):
         matches = self.vpcs.values()
         if vpc_ids: