Check that the epel repo exists before adding it

The epel repo that contains cloud-init and other packages needed for the
rackspace resource does not always exists. The setup script will fail if
you try to import the repo when it exists because of running the script
with set -e.

Change-Id: If1f912c2e7cbe3ccd58e10d0ea2e1e07b2114b48
Merge "Check that the epel repo exists before adding it"