Fixes setup.sh pxebr checks

Bug where pxebr was checking for link state UP before the subinterface
was added to the bridge.  Moved the check to be after.  Added a short
sleep in between issuing the link up and checking link status.

JIRA: OCTO-109

Change-Id: I7f782a35adf49b0da675e932d109c41b26016a5b
Signed-off-by: Tim Rozet <trozet@redhat.com>
(cherry picked from commit 87157c0dc9bd2a3da709d1cf980cce2e9c5469a3)