Rally doesn't apply changes to remote.repo.url when the src directory has data in it

[Simon Cooper]

1. Run a rally test with the default remote.repo.url
2. Change the remote.repo.url
3. Reference a branch or revision just on the new repo

Rally will continue to try to use the old repo url (as it has already checked it out into the src directory), and not find the specified branch/revision

Instead, when rally spots the checked-out code version doesn't match remote.repo.url, it should delete & re-fetch, or add a new remote, to the src directory