tests: Store the loopback images for test outside unit-tests

This directory is copied to each test prefix which is really
slow with the large loopback mounts.
Always start tests from a clean set of loopback images

This way we don't get any issues with leftovers
DeviceSet: Add UnmountDevice()

Right now this does nothing but add a new layer, but it means
that all DeviceMounts are paired with DeviceUnmounts so that we
can track (and cleanup) active mounts.
deviceset: Cleanup device sets on test end

We unmount all mounts and deactivate all device mapper devices to
make sure we're left with no leftovers after the test.
graph test: Unmount image via image.Unmount()

This helps us track the unmount
Runtime: Only remove device on destroy if it exists
api_test: Fix PostContainersCreate

We can't look for the created file in the rwpath, because that
doesn't exist in the device-mapper world, instead look in the
RootfsPath.
image: Fix error in unmount

We were returning err if it was nil, not the other way around
Container: Inject into the mount, not the rwPath

For device-mapper setups we can't just push the file into the rwPath.
basic libvirt-lxc support

This is a hack to start up a container using libvirt-lxc on Fedora 19.
It's just a proof of concept and needs a lot of work: console
integration, networking, and general cleanup.
libvirt-lxc: fixes for basic support

- Add virsh "--console" option to enable attached mode, and to allow
  logging in detached mode.
- Force -i and -t docker flags on.  These are required for "virsh
  --console" to work.
libvirt-lxc: dockerinit sleep hack

Sleep in dockerinit to give "virsh --console" a chance to start reading
the container's stdout.
libvirt-lxc: networking support

- setup ip address from dockerinit
- bind mount /etc/resolv.conf
libvirt-lxc: fixes for basic networking

Fix the interface type to 'network' in the libvirt xml template.  This
fixes the networking and allows multiple containers to run concurrently.

Currently it's using libvirt's virbr0 bridge interface.  We'll need to
change it to use the docker0 bridge by creating a new libvirt network.
FIXME