Add validation of the route before visiting

Add validation against the standard router object to ensure that
when we call session->visit($url) we provide feedback rather
than a false positive with 404s returned for missing routes.

The exception also include the correct XML config that is required
to pass this error.
Correct path and add alternate suggestion for CMS path
Fix typo
Merge pull request #33 from MageTest/feature/enhanced-route-excpetion

Add validation of the route before visiting