toaster-tests: fix tests for latest Selenium version

toaster-tests: fix tests for latest Selenium version

Previously, we didn't specify a specific version of Selenium.
When upgrading to Python 3 and installing Selenium to work with it,
the JS unit test broke, as the report format produced by Selenium
had changed.

Modify the test so that it works with the latest Selenium report
format.

Add a note to the README that the given Selenium version should
be used to prevent unexpected test failures.

Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>