votequorum: Fix up quorum/nodelist callbacks

votequorum: Fix up quorum/nodelist callbacks

This patch tidies the two state change callbacks and explains them
in the man page:

The difference between votequorum_nodelist_notification_t and
votequorum_quorum_notification_t is subtle but important.
The 'nodelist' callback is sent at the start of a cluster state
transition and contains the new ring_id and only the list of
nodes that are included in the sync state - ie only active nodes. No
quorum information is included this callback because it is not
available at that time.

The 'quorum' callback is sent after the cluster state transition has
completed and does contain quorum information.
In addition, the nodelist contains a list of all nodes known to
votequorum (whether up or down) and their state as well
as information about the quorum device attached (if any). quorum
callbacks will not be sent for qdevice up and down
events unless they affect quorum.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>