Add support for Docker as Nova hypervisor

* Add basic support for hypervisor plugins in lib/nova_plugins
* Add lib/nova_plugins/hypervisor-docker to use Docker as a Nova
  hypervisor.
* Add tools/install_docker.sh to install the Docker daemon and
  registry container, download base image and import
* Configure Nova to use docker plugin
* Add docker exercise and skip unsupported ones

Nova blueprint: new-hypervisor-docker

Change-Id: I9e7065b562dce2ce853def583ab1165886612227
diff --git a/clean.sh b/clean.sh
index f7d15df..a443ac8 100755
--- a/clean.sh
+++ b/clean.sh
@@ -64,6 +64,11 @@
 cleanup_neutron
 cleanup_swift
 
+# Do the hypervisor cleanup until this can be moved back into lib/nova
+if [[ -r $NOVA_PLUGINS/hypervisor-$VIRT_DRIVER ]]; then
+    cleanup_nova_hypervisor
+fi
+
 # cinder doesn't always clean up the volume group as it might be used elsewhere...
 # clean it up if it is a loop device
 VG_DEV=$(sudo losetup -j $DATA_DIR/${VOLUME_GROUP}-backing-file | awk -F':' '/backing-file/ { print $1}')