Add fedora support

The previous loop iterating usernames doesn't work if another user is
added as we move onto the second username once ssh comes up and root
fails to run a command and then hit a timeout on the second user and
never attempt the 3rd.

Instead take an approach there we continue trying root until it either
works or ssh succeeds but a command can't be run. At this stage we can
try any other users that may be configured on the image, with a short
timeout (as we know ssh has come up, if it hadn't ssh'ing as root would
have timed out).

Change-Id: Id05aa186e8496d19f41d9c723260e2151deb45c9
Merge "Add fedora support"