config: Reorganise the config system

To be more reliable & maintainable

The basic plan here is to fix reloads to be more stable
using read/parse/verify/build/commit stages, so that any errors
will not leave corosync in an unstable state. This should
also make the code more maintainable as currently the verify/commit
stages are horribly intertwined.

Also:

• Fix local_node_pos not being updated in the new map during validation (broke adding and removing new nodes in the middle of the list).
• Fix reconfiguration so that nodes are indexed by nodeid and not their position in the list. This is an old bug that's just been carried over

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>