Issue and workaround for installing foreman-proxy 1.2 via yum repo

A few ruby gems (and rubygems) that are required for foreman-proxy 1.2 to
install are not currently present in the yum repo. This has been reported
as an issue - if you're experiencing this bug, check out this issue for a
workaround. Bug #2744: rubygems removed from the foreman yum repo - Foreman