Fix error on first run after iOS simulator update

[ashleyplusplus]

Added logic to the JSON parser in subprocess.py to grab everything from the first { forward. This makes sure that it's only parsing- for lack of better phrasing- parseable stuff instead of just trying to parse the entire output, which contains "Install started, 1%... " on the first run after an iOS simulator update. Fixes #780.

PR Checklist:

• [ ] All new features have been tested
• [ ] All new features have been documented
• [x] I have read the CONTRIBUTING.md file
• [x] I will abide by the code of conduct

[ashleyplusplus]

I haven't installed my iOS simulator yet (new laptop), so I'm planning on testing by installing my simulator and running this.

[phildini]

Hoisting up the test failures:

tests/integrations/subprocess/test_json_parser.py::test_json_parser_fail[This is a prologue in my JSON output :( \n\n{"key": "value"}1] FAILED [ 65%]```

[freakboy3742]

Closing on the basis this has been stale for over a year. Thanks for the contribution; the general approach looks promising, and someone else might be able to use this as a starting point.