refactor _get_sync_routers to use get_routers.

By using get_routers, get_sync_data() can get all attributes
including attributes provided by extensions which extend router ext.

Change-Id: I4be761dadd18eed19f4e54676e77d99bcc4a4745
Perform a joined query for ports and security group associations

bug 1174111

Instead of loading security group associations with a separate query
each time a port is loaded from the database, perform the load operation
with a join using a joined sqlalchemy relationship.
Also, this patch removes the need for invoking the mixin method
'extend_port_dict_security_group' from the plugin code.

Change-Id: I40b22281d45ff4f4bf8149211883799a9051c1a0
merge https://review.openstack.org/#/c/24969/
merge multihost mode https://review.openstack.org/#/c/24771/
add /32 subnet support
make external network working when namespaces disabled
Merge pull request #2 from hyunsun/feature/ngmodel

Merge multihost mode to 2013.1.2