libglusterfs: Fix valid_host_name for consecutive dots

The valid_host_name() function must reject addresses with consecutive
dots in them.

Change-Id: I1749de80c66e8fbad63b2e014f79e0203906030e
BUG: 977246
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/5249
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>