pybind/mgr: index=4, sort_keys=True for json.dumps throughput

pybind/mgr: index=4, sort_keys=True for json.dumps throughput

- fixes balancer test on py3 by making the pool ls order deterministic
- makes everybody else behave consistently

I left internal json storage alone--no need to sort/normalize.  I also
left out some CLI commands returning non-indented json.

Signed-off-by: Sage Weil <sage@redhat.com>