webadmin: Fix NPE in cluster gluster services view

Some of the gluster services may not have port number present,
so adding null check for it.

Change-Id: Ic6c69207238d7553abafbcb9c1ffe7eb81897e64
Bug-Url: https://bugzilla.redhat.com/885592
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>