geo-rep: calculate worker distribution scheme

- monitor: fetch and parse volume info, both local and remote
- gsynd.c: allow volume info request
- monitor: calulate local brick/remote node pairing a'la xsync
  - two variants actually:
    - default mode assumes master and slave is on the same network
      and that we can ssh directly to particular slave nodes
    - with "isolated-slave" mode we keep the originally
      given host as ssh target, and only within that host
      we specify gluster access to the various slave nodes

For now we don't make any use of the resultant pairing,
just log it.

Change-Id: I2a4239ac1761f75c4385c3a89815d0643de52d14
Signed-off-by: Csaba Henk <csaba@redhat.com>