Rename guestIF{,Tests}.py to guestagent{,Tests}.py

Change-Id: I9f3f2068dd8f61538d76687cbf0c55c85d8eeb6e
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26195
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Francesco Romani <fromani@redhat.com>