Added tests for invalid usages of the drivers

These tests cover calling the driver for XPath not matching elements on the page (case which should not happen in normal usage of Mink given that the driver is accessed from found elements most of the time) or for XPath matching an invalid element (trying to check a div for instance).
These tests ensure that a DriverException is thrown rather than doing an undefined behavior (potentially a fatal error).

Refs https://github.com/Behat/Mink/issues/473 and https://github.com/Behat/Mink/issues/467