Add proxy client tests

[ehelms]

This re-uses the existing client tests but runs them separately against a proxy to ensure that any changes in the mechanisms on the proxy are warded against regressions. This requires the ordering to a bit different as we need to ensure the Test environment is synced on the proxy and that hammer is configured. The current setup of hammer on the proxy is admittedly a smidge ugly. The installer scenario for foreman-proxy-content and others does not have the cli classes available to it for configuration through the installer. I could implement a hammer CLI role to capture this configuration.

My goal was to get as quickly as I could a test online for clients against a proxy with content and some initial work.