It is not currently possible to deploy Bifrost on a host other than the
Ansible control host. A deployer may want to manage an Ansible control
environment remotely from the Bifrost deployment host but is currently
unable to.

This change adds a new top level 'deployment' Ansible group and a
'bifrost' Ansible group containing the 'deployment' group. The Ansible
play in ansible/bifrost.yml is now targeted at the hosts in the
'bifrost' group. For backwards compatibility, the all-in-one and
multinode inventories add localhost to the deployment group. This allows
a deployer to deploy Bifrost on a remote host by modifying the hosts in
the deployment or bifrost groups.

Change-Id: I76808feab5dd67dff63379ed9c7d08a105636acf
Closes-bug: #1665373