In playbook.yaml, support vault_password

[djha-skin]

This issue is a feature request.

When I call the ansible.playbook command, I want to be able to specify the vault password without using a vault password file. That way, I can set the vault password in the stackstorm key/value store and use it from a rule like this like this:

action:
    ref: "ansible.playbook"
    parameters:
        playbook: "playbook.yaml"
        vault_password: "{{ st2kv.system.vault_password }}"