Fix json output appending

The json output wasn't doing its read/append/write cycle properly,
leading to:

  {
    "plays": {
        "plays": {
            "plays": {
                "plays": {
                    "plays": {
                        "plays":

Which, while amusing, isn't really what we wanted.

Add a wrapping layer that contains playbook info. The original format
has a list of play results but only one stats section, so it's not
actually suitable for appending a list of plays anyway.

Change-Id: I49394e9faa8027a21e5ef6919c0f75a4473f51a9
1 file changed