Retrying to instantiate a browser when getting error status 13 from wd

Sometimes when trying to instantiate a completely legitimate platform and browser combo you still get an error from saucelabs that says that the environment can't be set up for some reason. Zuul verifies that each tried setup is available before even trying to instantiate such a browser, so we can safely catch that error and retry to instantiate the browser when we get this error. Not quitting on this error should save us some trouble with e.g. travis builds.

The PR checks for two kinds of errors, because the same error can essentially be thrown as a slightly different error in two places. One of them is here: https://github.com/admc/wd/blob/master/lib/webdriver.js#L127 and the other is here https://github.com/admc/wd/blob/master/lib/callbacks.js#L26.