Only call qb_ipcc_disconnect when the instance is fully dereferenced.

Sometimes calling xyz_finilize() within a dispatch would
cause a crash because the qb_ipcc_disconnect actually
disconnects immediatly and frees it't memory. whereas
the corosync structure is reference counted. So this
makes use of the reference counting to only call
qb_ipcc_disconnect when it is fully dereferenced.

Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>
Signed-off-by: Angus Salkeld <asalkeld@redhat.com>