[#4] Install git before trying to use it; add a unit test for cloudfoundry_source so that hopefully we can catch other problems.

Unfortunately git is installed by test-kitchen itself so we wouldn't have noticed anyway.
Cleanup: do not create bundler directories ourselves, bundler will.

Not sure why at some point in the past I thought it was necessary; maybe some bug that I've since fixed.
Release 1.3.2: fix missing dependencies.