nfs/auth: reject mounts if getaddrinfo fails

When nfs.addr-namelookup is turned on, if the
getaddrinfo call fails while authenticating client's
ip/hostname, the mount request is denied

Change-Id: I744f1c6b9c7aae91b9363bba6c6987b42f7f0cc9
BUG: 947055
Signed-off-by: Rajesh Amaravathi <rajesh@redhat.com>
Reviewed-on: http://review.gluster.org/5143
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>