json result file

[Trask Stalnaker]

Hi,

The json result file is currently written using the default platform
encoding, which is a bit troublesome when parsing since json parsers (at
least Jackson) assume the file is always UTF8/16/32.  (in particular I ran
into issues with the metric name prefix "\u00b7")

On a separate issue, the newlines inside some of the attribute names make
programmatic parsing less convenient (even though valid json), e.g.

        "secondaryMetrics" : {
            "·gc.churn.{
                PS Eden Space
            }
            " : {
                ...
            },

The new gc churn metrics themselves are awesome though.

Thanks,
Trask