Move the playbooks/inventory folder, group_vars, and host_vars to
inventory/ in the root of the OpenStack-Ansible repo. This helps better
organize the repo structure since playbooks/ will now only contain
playbooks, shared task files, and included repo package var files.
group_vars and host_vars are moved alongside the inventory since that's
the default place that Ansible expects those folders and to help better
prepare for Ansible 2.4 where multiple inventories can be loaded,
automatically including relative group and host var files.
Effected docs, scripts, and variables have been updated with the new
paths.
Change-Id: If50e2412c3fd6575d7041deb8ecc9480b04184cc
c5551f2c8c