Remove vcloud-tools-testing-config BEFORE tests

Tell `git clean` to remove untracked git repositories before fetching
vcloud-tools-testing-config. Although 6232186 was a good thing to do, it
didn't solve the immediate problem of the directory existing in our
workspaces right now, only after a successful clone.

I've removed the `rm -f Gemfile.lock` because it's covered by `git clean`
(as the file isn't tracked and the `-x` says to disregard `.gitignore`).
Merge pull request #61 from alphagov/really_remove_testing_config_repo

Remove vcloud-tools-testing-config BEFORE tests