Standardize creation of rpcapi client instances

This cleans up where the get_foo_api() is placed, so it's only placed in the
respective svc.rpcapi.SvcApi.get_instance() vs in multiple locations.

Change-Id: I75ce3f17f892a619889f7d3a0a8f66c1ff788849
Merge "Standardize creation of rpcapi client instances"