HPCC-8803 Directories hpcc-data2 and hpcc-data3 don't get used

Roxie should specify for each slave/channel what replication level it
represents, and then pick up from the standard directory locations
information.

Extend the named group store to retrieve information about the type of a
group.

Use per-channel caches to minimize work of file lookups (as calculating remote
names - even when they are then not needed - can get expensive).

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>