many commands seem to have sort of had
stopped following the expected convention
in `mc` to differentiate *probe.Error.
To keep things readable this PR is the
first attempt at such a cleanup.
Change the JSON output of mc support perf
The new change will still print multiple JSON lines for each conducted
performance test but now we have a new field called 'type' field to
difference between network, drive and object tests.
This change also adds 'final' field to indicate this is the final json of a
particular performance testing.
Also, errors when conducting those tests will have a field 'err' as well
in the JSON output.
