Install docker python module with pip

The docker-py python module is now called docker and has an
incompatible api. Running latest kolla-ansible with docker-py
will throw an error like this:
AttributeError: 'module' object has no attribute 'APIClient'

Change-Id: Idd10735c764717cf711f62b3243d39d8c8ed263f

doc/quickstart.rst

@@ -228,17 +228,8 @@ Restart Docker by executing the following commands:
     systemctl daemon-reload
     systemctl restart docker
 
-On the target hosts you also need an updated version of the Docker python
-libraries:
-
-.. note:: The old docker-python is obsoleted by python-docker-py.
-
-::
-
-    yum install python-docker-py
-
-
-Or using ``pip`` to install the latest version:
+On the target hosts you also need to install the latest version of the Docker
+python libraries with pip:
 
 ::