Ensure epel7 is installed only on rhel7/centos7

Change-Id: I5812812f7d2cb5ba2e310e33d6e01cda8823c1c4
Merge "Ensure epel7 is installed only on rhel7/centos7"
Do not try to detach non-existant loopback devices

A user reported symptoms where the losetup line used to detach the
loopback device was failing in tar mode. We don't need to detach a
device that does not exist.

Change-Id: I807996e16199288927b49b4f300ae9b461cb8fe7
Closes-Bug: #1378033
Merge "Do not try to detach non-existant loopback devices"
iso element

Change-Id: If76a22e72ff842c53022a054796c12db1ad2c0c5