Fix the SaltStack setup of the Docker subsystem.

The move to support Centos on GCE is a good thing, and I would like to help this effort out.  

The initial Salt scripts were authored to be a single environment, single OS platform, and they have grown somewhat organically.  When I added support for a Vagrant Fedora cluster, I had used if blocks os_family != RedHat and os_family == RedHat as a means of distingushing this environment.

We can no longer do this if we add support for Centos on GCE.

Cloud Provider | Operating System | Details
------------ | ------------- | -------------
gce | debian | need to do networking the GCE way
gce | centos | need to do networking the GCE way
azure | debian | this is what the MSFT guys appear to test
azure | centos | no one has thought about yet
vagrant | fedora | added as new cloud_provider in #851, need to look at networking per #833 
none | fedora | this is current vagrant setup which just lists machines explicitly

So in essence, any networking decisions need to be cloud_provider specific.  In this instance, it needs to only do this network setup when on gce or azure, but not vagrant and not when grain.cloud_provider is not defined (as in the current vagrant setup).