Currently devstack assumes that the network used for ssh validation is the private network. This patch adds a hook that sets the network used for ssh validation based on whether or not provider networking is being used. It also moves the function 'is_provider_network' into functions-common as it will now be used by both tempest and neutron. Change-Id: I265c9e26c9bfb18b7e201f27d8912b8bec235872