Install openstack.kolla collection

This change adds an Ansible Galaxy requirements file including the
openstack.kolla collection. A new 'kolla-ansible install-deps' command
is provided to install the requirements.

With the new collection in place, this change also switches to using the
baremetal role from the openstack.kolla collection, and removes the
baremetal role from this repository.

Depends-On: https://review.opendev.org/c/openstack/ansible-collection-kolla/+/820168

Change-Id: I9708f57b4bb9d64eb4903c253684fe0d9147bd4a