Software-config hook for ansible

Added ansible to the software-config README

Created a new folder elements/heat-config-ansible that will be
pre-installed by diskimage-builder on any images wishing to use the
ansible hook.

Created an example ansible heat template with an example ansible
script as a starting point.

Updated README.rst to reflect how heat-config-ansible interacts with the HOT template.

Change-Id: I861e96186e2f5d5b65ea5100edf1b82e753c425c
Merge "Software-config hook for ansible"