Note that this includes seemingly-unrelated test changes because we
were actually skipping the snapshot_running test for libvirt, which
has been a bug for years. In that test case, when we went to look
for image_meta.disk_format, that attribute was not set on the o.vo
object, which raised a NotImplementedError. That error is also checked
by the test to skip the test for drivers that do not support snapshot,
which meant that for libvirt, we haven't been running that case
beyond the point at which we create snapshot metadata and trip that
exception. Thus, once removing that, there are other mocks not in
place that are required for the test to actually run. So, this adds
mocks for qemu_img_info() calls that actually try to read the file on
disk, as well as the privsep chown() that attempts to run after.
Change-Id: Ie731045629f0899840a4680d21793a16ade9b98e
d5a631ba77