Fix edit-node to work with repos again

Pull the right filename out of mkstemp() instead of a tuple, don't
blindly check for file://, which can also match GPG keys, make
sure we actually find a file-based repo before we try bind
mounting

Change-Id: Ic6751fac97cf8e094815a2a4477f340ca422e4bf
Signed-off-by: Ryan Barry <rbarry@redhat.com>