Modified provision_cf so that it clones the cf-release repository.

This PR is a replacement for the PR associated with https://www.pivotaltracker.com/story/show/74733740.  After many mistakes using git, I gave up and completely redid my fork, and thus needed a new PR.  Previously, collaborators had said:

@programsam Thanks for the PR.

    The git URL does not look correct - shouldn't it be https://github.com/cloudfoundry/cf-release
    What if someone already has cf-release checked out and wants to use that specific version?

To the first point: I have fixed the URL, thank you.

To the second point: I created this PR to help address https://github.com/cloudfoundry/bosh-lite/issues/110 because the error message was occurring because I hadn't cloned the cf-release directory.  This seems like the most logical response.  However, the script appears to (https://github.com/cloudfoundry/bosh-lite/blob/master/scripts/provision_cf#L41) always look for the most recent CF release.  So if you checkout v169, for example, the script should obtain the release.yml for 169.
please change to `clone_cf`