Change NeutronWorkers default to result in previous behavior

Change NeutronWorkers default to result in previous behavior

Neutron's behavior changed in Newton with respect to the default value
of 0 for NeutronWorkers. Instead of effectively treating it as
"processorcount", it now assumes we mean what we say and doesn't spawn
any workers, resulting in only a single process for handling API
requests. This change alters the default value to regain the previous
behavior.

This change also extends the worker count to the RPC worker setting -
which was possibly an oversight in previous releases. The default
behavior will have no result for most systems.

Closes-Bug: 1619383

Change-Id: Id6e3ee544160372c806905e77348150a1a1eec1b