Ansible: Improvements for 'extra_vars' argument

`extra_vars` argument can now:
- contains a hierarchical set of parameters (instead of flat Key-Value Pairs)
- alternatively refers to a configuration file (instead of embedded Hash)

See Ansible Documentation for version requirement details:
http://www.ansibleworks.com/docs/playbooks_variables.html#passing-variables-on-the-command-line
core: Allow hooking before and after provisioners
core: Improve provisioner hooking by introducing a new builtin action for wrapping provisioner runs
core: Fix action name used for ProvisionerRun
website/docs: document environmental variables
core: fix exception case regression from yesterday
communicators/ssh: pty can be enabled
core: allow hooks to send arbitrary data
core: expose the hook method from the env
core: allow custom callables in hooks
Merge pull request #2405 from fgrehm/2044-provisioner-hooking

core: support hooking around provisioners runs
core: allow hooking around provisioner runs

/cc @fgrehm - :) I think you'll understand.
Merge pull request #2366 from gildegoma/ansible-extra-vars

provisioners/ansible: Improvements for 'extra_vars' argument
update changelog