vacuum: correctly send TRY_DELETE_RECORDS ctrl to all active nodes

vacuum: correctly send TRY_DELETE_RECORDS ctrl to all active nodes

Originally, the control was sent to all records in the vnn_map, but
there was something still missing here:
When a node can not become lmaster (via CTDB_CAPABILITY_LMASTER=no)
then it will not be part of the vnn_map. So such a node would
be active but never receive the TRY_DELETE_RECORDS control from a
vacuuming run.

This is fixed in this change by correctly building the list of
active nodes first in the same way that the recovery process does it.