Ugly format of data in outputReport.json

[pawelpasterz]

commonArgs -> data is printed as a single-line string let's have it written in the form of JSON

"args": {
    "commonArgs": {
      "data": "---\ngcloud:\n  app: \"app-debug.apk\"\n  test: \"app-multiple-success-debug-androidTest.apk\"\n  directories-to-pull:\n  - \"/sdcard/\"\n  num-flaky-test-attempts: 1\n  use-orchestrator: false\n  timeout: \"15m\"\n  performance-metrics: false\n  record-video: true\nflank:\n  max-test-shards: 2\n  shard-time: \"120\"\n  additional-app-test-apks:\n  - test: \"app-multiple-success-debug-androidTest.apk\"\n    test-targets:\n    - \"class com.example.test_app.foo.FooInstrumentedTest\"\n    - \"class com.example.test_app.bar.BarInstrumentedTest\"\n    device:\n    - model: \"Pixel2\"\n      version: 28\n  - test: \"gs://flank-open-source.appspot.com/test/app-multiple-success-debug-androidTest.apk\"\n    max-test-shards: 5\n    device:\n    - model: \"Nexus6P\"\n      version: 27\n  ignore-failed-tests: false\n  full-junit-result: false\n  output-style: \"single\"\n  disable-usage-statistics: true\n  legacy-junit-result: false\n  output-report: \"json\"\n",
      "devices": [
        {
          "model": "NexusLowRes",
          "version": "28",
          "locale": "en",
          "orientation": "portrait",
          "isVirtual": true
        }
      ],