Refactor the git-lfs checking: this means both clearer code in the download()
function and allows unit testing to monkeypatch the functionality.
(Bitbake rev: 33cf9172ded50a869f7201ba463ab9ecc69b8252)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>