Ensure keystone endpoint set before service starts

As neutron-server is mostly useless without having the keystone
service+endpoint set, in the case where both keystone and
neutron-server are on the same machine, this patch adds a soft
dependency to ensure that the keystone catalog includes neutron

This has a knock on effect of fixing openstack::provisioner, which
would sometimes try to create neutron networks, the type for which
soft depends on neutron-server, without there being an endpoint
set in the keystone catalog

Change-Id: I658e1b3e2c448b9a7da9e013c4e105b9ec824893