fix(wd): get sessionId from driver instead of promise resolution

The sauce reporter is not working (I guess for a while now) since the sauce launcher is not storing the jobId correctly. Since the `init` callback in `wd` has two parameters (`sessionID` and `capabilities`), the promise resolution is actually an array of two arguments, so the `jobId` is actually `args[0]`, but I thought it would be better to just use `driver.sessionID`.