Add detach_vpn_gateway, add VPN gateway tests
Add VGW Route propagation tests
Add VPC internet gateway tests
Move VPC network acl tests to own file
Add VPC DHCP options tests
DeleteVpc and ModifyVpcAttribute tests, PEP8
Add VPC subnet tests
Add CustomerGateway tests, PEP8, fix bgp_asn type
VPC RouteTable fixes and tests, pep8

* Return newAssociationId in replace_route_table_assocation
* Allow create_route to take network interface_id
Indentation VPC PEP8 fixes
Route table assoc backwards compatibility