glusterd: Rename the export dictionary as peer_data

During a glusterd handshake, a dictionary is passed among
the peers which contains, info of volumes, global opts,
and now also info of snaps and list of missed snaps

As it now contains more than just volume specific data,
renaming the dict in the code-base from "vols" to "peer_data"

Change-Id: Ib457172789ddd0d8978b08bceab0988c48e9eea7
BUG: 1061685
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/7524
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>