Disable live-RPC queries under split query

Currently, the node listing RPC is very slow due to missing
parallelisation. For the 2.7 release, we reset these back to masterd,
hoping to revert them by the time 2.8 is ready.

There are a number of queries that I've left pointing to confd, as
they are non-RPC:

- node fields query
- node static fields query (and added a note in one case where it
  could become a problem)

All the other converted queries (job listing, group queries, tags,
cluster config) remain pointing to confd, as they don't use RPC.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>