Split client config file into a separate class so we can interface directly with it.

Summary:
Since openvpn::client depends on openvpn::server it is not appropriate to use it
it to manage client configurations on an openvpn client. I broke the config file
portion of openvpn::client into openvpn::client::config so we can access it directly.

Ref T44.

Test Plan: Tests good via rake spec

Reviewers: #developers, pfrost

Reviewed By: #developers, pfrost

Subscribers: pfrost, jbowman

Maniphest Tasks: T44, T35

Differential Revision: http://phabricator.macprofessionals.lan/D42