doc: Fix peer probe deficiencies

Added the command to probe the first server to assign it a hostname

Change-Id: If59457a2cbbb362f706d0898ed2b84d4c76bdc0d
BUG: 1095595
Reviewed-on: http://review.gluster.org/7853
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>