add check for test that errors before even starting a job

[rubensayshi]

fixes #177

when saucelabs cant start a job for a test it will error with:

{ completed: false,
  'js tests': 
   [ { status: 'test error',
       platform: [Object],
       id: '7c738f49617046b79f6d3660c0668053',
       job_id: 'job not ready' } ] }

this should be caught because atm it's causing an infinite loop until canceled (with attempts is set to -1).

this likely occurs when you're trying to specific a platform / version that saucelabs doesn't have, for example I ran into this with:

{
        browserName: 'firefox',
        platform: 'Linux',
        version: '47'
}

unfortunately I can't really figure out how your tests are being ran, so can;'t add a test for this :(