Foreman » Smart Proxy

Fixes #10259 - Templates are now fully proxied

It was ignoring some parameters (MAC for bootdisk) as well as headers
(HTTP_X_RHN_PROVISIONING_*).

Originally written by William Hefter, but completely redone from scratch.

Refs #8267 - pass template_url in call to foreman

Also passes the ?static parameter on correctly

fixes #8300 - set webmock custom HTTP status response correctly

Refs #969 - Proxy-side changes for serving templates from the proxy

An update to @GregSutcliffe's original PR. Ports his original feature to the new
plugin api.