ctdb-tools: Add cross-node file comparison to "reloadnodes"

ctdb-tools: Add cross-node file comparison to "reloadnodes"

This compares the nodes file on the current node with that on all
nodes.  If any are different then do not reload nodes.

If any nodes files can't be fetched then do not reload nodes.  This
could be because some nodes are running an older version without this
feature.  This is unsupported: why make a major cluster
reconfiguration while a cluster is half upgraded?

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>