webadmin: display N/A for gluster services port if not applicable

'SHD' services may not have port numbers and it will be displayed
as 'N/A' if portNo is 0.

Change-Id: I92485213c23ed26742b70db26c1230ea662bc0e5
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>