Ansible debugging - switches allow stop before Ansible config generation and execution

[markllama]

This change offers switches to developers to control the stack processing. It replaces one existing switch and adds one other.

• The prepare_ansible switch replaces and inverts the skip_ansible switch
• The execute_ansible switch is added.

Both switches default to true and are used only for development and debugging of the heat stack

= New Behavior

== prepare_ansible
When true, the stack script generates the ansible configuration scripts which will be used to install OpenShift on the target instances.

When false the stack script exits with success but stops processing before generating configuration or executing the ansible playbooks.

== execute_ansible
When true the stack script executes the openshift-ansible playbooks to install OpenShift on the target instances.

When false the stack script stops before running the playbooks and reports the ansible-playbook command which would have been executed.

When prepare_ansible