libglusterfs: avoid the logging which says the port is invalid

If the reserved ports file in proc contains just a newline, then
do not proceed with ports checking and reserving.

Change-Id: If610b0e49a97e5c22e7e2b1bb4155c9616a4612a
BUG: 762989
Signed-off-by: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-on: http://review.gluster.org/4583
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>