Support arbitrary cache stores in Origin

Allow cache stores to be configured in the broker and console via the "CACHE_STORE" config value.  Clients wishing to use a specific cache store may have to ensure the Gem is loaded by adding a plugins.d/<gemname> file corresponding to their desired client.

Example config is Dalli:

    CACHE_STORE=:dalli_store, 'localhost:11211', {:namespace => 'console', :failover => true, :expires_in => 1.day, :compress => true}

and you would create an empty file at

    /etc/openshift/plugins.d/dalli.conf

so that the broker loads Dalli.  For the console, you'd need to change the Gemfile (we don't have a gem extension method for the console yet).