Merge pull request #17 from Cerberus98/master

Implements #3669
Fixes RM2442 VIF ordering

Ports should now be ordered by created_at.
Merge pull request #18 from rackerlabs/rm_2442

Fixes RM2442 VIF ordering
Fixes #19

Wraps all session using plugin calls in a decorator that automatically
closes the session and resets the context session state to None.
Merge pull request #20 from Cerberus98/closed_sessions

Fixes #19
Fixes #21

Previously, --no-gateway wasn't being honored correctly. Instead of not
creating a route as intended, the correct representation of a gateway
for a subnet, we were creating a default route with CIDR 0.0.0.0/0 and
NULL gateway. This patch allows gateway_ip == NULL to be passed and
handled appropriately.
Merge pull request #22 from Cerberus98/issue21

Fixes #21
Fixes #23

Route find by way of route delete is now being passed the "id" argument
correctly, preventing us from deleting the wrong route.