No error for failed commands.

[LeachBogdan]

Right now the driver doesn't throw any error when the server returns a non-zero status for a json call. This makes it very difficult to debug tests as the failure is just a general timeout with no indication of where it originated or what actually timed out; for example, if I'm locating the wrong element or for some reason it's not in the page yet, the "no such element" response of the server should be interpreted and thrown as an error (complete with stack trace hopefully).