Merge pull request #172 from Cerberus98/master

Adds Network extensions resource
Allows easier configuration of default networks

Updates the Quark networks extension to allow the id and ipam_strategy
to be passed along with a network create. The id is specifically gated
as admin only, but as an admin, allows deployers to configure special
networks like the all 0s and 1s placeholder values we use at Rackspace.
Merge pull request #173 from Cerberus98/r2965_squash

Allows easier configuration of default networks
Fixes #174

Updates the ipam_strategy handling to allow not passing ipam_strategy
again.