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/exercises/sec_groups.sh b/exercises/sec_groups.sh
index 6b67291..7d80570 100755
--- a/exercises/sec_groups.sh
+++ b/exercises/sec_groups.sh
@@ -33,6 +33,9 @@
 # Import exercise configuration
 source $TOP_DIR/exerciserc
 
+# Skip if the hypervisor is Docker
+[[ "$VIRT_DRIVER" == "docker" ]] && exit 55
+
 
 # Testing Security Groups
 # =======================