Decouple cache_server from build server

These commits allow the cache server to be
deployed separately from the build server.

Previously, it had accidental depdenencies on
a few things from the monitoring_server profile:

- needed it to include apache
- relied on its python twisted package being installed

This commit fixes things so that cache_server can be
deployed on its own.
Add openstack client deps for auth_file

Previously, the auth_file component was deployed
without any depedencies.

The reality is that the file only makes sense when
deployed together with the relevant openstack clients.

This patch adds openstack::base as a dep as well as
openstack::client.
Add build_server::test role

This commit adds a new role called build_server::test

This role serves as a normal build server, but also
installs the openstack client libs so that it can
actually run the test file and connect to floating ips
from an external machine.
Add a cache role.

This commit adds a role that only configures a cache server.