Add Ansible executor class for node context

Add Ansible executor class for node context

import the AnsibleCommon class to execute Ansible playbooks

Update node context support to use AnsibleCommon

needs unittests

We must call ansible-playbook as an executable, so we must create temp
files for inventory, and for the playbooks.

AnsibleCommon has evolved to be quite flexible, it auto-generates the
inventory from the context['nodes'] and generates groups from the node
Role.

We also support either a single playbook filename, or a list of
filenames.

If given a list we dynamically generate a playbook that includes the
other playbooks.

We support adding any number of extra_vars using a temp JSON file.

Also designed to be extended by subclassing.

Change-Id: I5bd0a2b4547feaadd70b7e2b8801f19371b99df0
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>