Fedora 20 is released, not devel

Change CUR_DEVEL to Fedora 21 to avoid livecd-tools instability

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1091693

Change-Id: I946fc23ddb7ad0202f0d24cfec310529548d0914
Signed-off-by: Ryan Barry <rbarry@redhat.com>