fixes #9614: update for GCEv1, adds disk and networking functions

Way back at the conference, I showed off some new salt-cloud + Google Compute Engine features.  This PR contains updates for GCE v1 public API and adds support for:
* persistent disks
* snapshots
* networks
* firewall rules
* load-balancer

It also includes `salt.utils.cloud.fire_event` triggers for all methods.

As usual, none of this work would have happened without the expert hand-holding by @techhat. :)