Add unit test for the xenapi plugin -glance and also add
a boolean return value to _download_tarball_and_verify
so that it's eaiser to check the result for this function.
This commit is for upload image and vhd
At the same time, fix the keyword error in _update_image_meta_v2
Change-Id: Idad364a4e10f6e19a3d2344baa00272da12de316