Init webdriver inside mocha setup function to avoid BrowserStack timeouts.

[rupl]

As mentioned in #81 (comment) this small change will save people a big debugging headache once they have more than 2 or 3 tests being initiated by mocha.

[christian-bromann]

@rupl thanks but I don't quite understand the enhancement of this PR. Who is timing out here?

[rupl]

My connection to Browserstack was timing out. Nothing was going wrong with webdriverio or webdrivercss, this is mostly just me fixing a "not thinking in async" mistake

Say I have 4 copies like this example file. When I send all the files to mocha, it would kick off 4 connections to BrowserStack instantly. Then webdrivercss would run them one at a time, so by the time it got to the third or fourth test, the 90-second BrowserStack timeout had been passed, and the tests at the back of the line could not complete.

By using mocha's before(), the individual BrowserStack connections are only opened when the test is finally being run. It's less resource intensive on their service, and avoids timeouts.

[christian-bromann]

Ohh now I get the point. Make sense. I hope this will get a lot easier once I hooked up WebdriverCSS with WebdriverIO v3. It will allow us to run multiple instances at the same time. Until then this is definitely the way to go. Thanks again