Gluster/Doc : Updated admin guide diagrams

Updated the diagrams for the sections on setting up
distributed replicated volumes and striped replicated volumes

Change-Id: I44ecd2aba75816fdb2f6324c4337cf5fb621ecae
BUG: 1113842
Signed-off-by: Nithya Balachandran <nbalacha@redhat.com>
Reviewed-on: http://review.gluster.org/8256
Reviewed-by: Ravishankar N <ravishankar@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Prashanth Pai <ppai@redhat.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>