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/README.md b/README.md
index 6426e9a..99e9838 100644
--- a/README.md
+++ b/README.md
@@ -12,10 +12,14 @@
 
 IMPORTANT: Be sure to carefully read `stack.sh` and any other scripts you execute before you run them, as they install software and may alter your networking configuration.  We strongly recommend that you run `stack.sh` in a clean and disposable vm when you are first getting started.
 
-# Devstack on Xenserver
+# DevStack on Xenserver
 
 If you would like to use Xenserver as the hypervisor, please refer to the instructions in `./tools/xen/README.md`.
 
+# DevStack on Docker
+
+If you would like to use Docker as the hypervisor, please refer to the instructions in `./tools/docker/README.md`.
+
 # Versions
 
 The devstack master branch generally points to trunk versions of OpenStack components.  For older, stable versions, look for branches named stable/[release] in the DevStack repo.  For example, you can do the following to create a diablo OpenStack cloud: