Add support for a 'skip' attribute on individual tests and test suites

[kkajla12]

This PR adds support for a boolean skip attribute to individual tests and test suites. If set to true, the attribute skips the given test/suite (defaults to false).

Skipping a test suite:

{
   "skip": true,
   "tests": [
      ...
   ]
}

Skipping an individual test:

{
   "tests": [
      {
         "name": "myTest",
         "skip": true,
         ...
      }
   ]
}