Revert "libvirt: support live migrate of instances with conf drives"

This reverts commit ecce888c469c62374a3cc43e3cede11d8aa1e799.

Using the image cache is the wrong way to move an image into the same
storage as other instance disks. We should just call into the relevant
backend store directly.

Change-Id: Id867b89d959c26d067cb06b52a496e2b98573289
do not use unittest.TestCase for tests

We setup a number of fixtures in nova.test that are part of our
expected runtime, including stdout / stderr capture. Fix a recently
committed unit test that was bypassing that.

Change-Id: Ia6c02f8dff7d910353121c51fe1ec97d0454809d
Merge "do not use unittest.TestCase for tests"
Merge "Revert "libvirt: support live migrate of instances with conf drives""