Ignore nova hosts with no network

If a host does not have working network, we should just skip it.
Move nova connection code to shared library
Use OpenStackCloud in nova modules
Prep OpenStackCloud for more than Nova
Replace factory method with function
Use nova_client in nova_compute
Split openstack options out into the module_utils
Rename OpenStackAnsibleException
Add glance support to OpenStackCloud
Use glance in nova_compute

If the glance endpoint is available, it's more efficient to use it
than to use the nova endpoint passthrough. Use the image listing
routines in OpenStackCloud to try glance first, then nova.
Rename service_type to nova_service_type

service_type is only settable at the moment in the inventory script,
and even there it's only for backwards compatability reasons. While we
want to be consistent, we don't want to _add_ backwards compat issues
into new places ... so make sure it's an optional class constructor
parameter and don't add it to any argument specs.
Make keystone_user use OpenStackCloud
Enable nova to process keystone tokens