glusterd: Authenticate management handshake requests

Backport of
  371bb42 glusterd: Authenticate management handshake requests
from master.

Management handshake requests, which are used to validate op-version
supported by the peers, are now only allowed if,
- the glusterd doesn't have any other peer, or
- the request was sent by another peer.

This prevents the op-version of a peer being changed because of a
connection attempt by an invalid peer.

BUG: 1144978
Change-Id: I5a909dad37e9873efe8b75dad41b7af71ce91c3d
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/8819
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>