common/Formatter: add dump_format_unquoted()

Sometimes a savvy caller wants to format the output but doesn't want it
quoted.

Signed-off-by: Sage Weil <sage@inktank.com>
common/perf_counters: fix missing decimal in time, quoting

We shouldn't quote integer or float values.  Also easier to use
dump_unsigned.

Signed-off-by: Sage Weil <sage@inktank.com>
common/perf_counters: fix unit tests

The commands are now in json.

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