If sys.exit is called or SystemExit raised, don't display success

If sys.exit is called or SystemExit raised, don't display success

If sys.exit is called, which raises SystemExit, the finally at the
end of the installer was treating it as a successful install and
displaying messages to the user. Catch this exception and mark
the install as failed to prevent this.

https://fedorahosted.org/ipsilon/ticket/66

Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>