webadmin: Show Guide Me before vNIC creation

There's no real need to wait for the vNIC creation to finish before
showing the Guide Me dialog; if the creation succeeds then it could
happen asynchronously while the user deals with the Guide Me dialog
(I'm unaware of any interdependence between the operations), and if it
fails then an error dialog will popup up anyway (and on top of the
Guide Me dialog rather than under it).

Change-Id: If4bebb56613ebaed67377489448501ba9642adf6
Bug-Url: https://bugzilla.redhat.com/1066461
Signed-off-by: Lior Vernia <lvernia@redhat.com>