Add element to install Openstack python-* clients.

There was no way to install openstack clients without installing boot-stack.
Elements like nagios need the clients but may be running on different nodes
other then then OpenStack control plane so should not install boot-stack.

Python-mysqldb was being installed twice, which is untidy and may slow things
down with some package managers.

Change-Id: Iaeecf88d781eb7adc4a903b8332e1a92eea5fe38
Authored-by: Chris Krelle <nobodycam@gmail.com>
Merge "Add element to install Openstack python-* clients."