In a homogeneous hardware deployment that uses the same ramdisk for all
nodes, and possibly the same playbooks for actions with ansible deploy
interface, it is benefitial to make defaults of various `ansible_`
driver_info fields to be configurable via ironic configuration file
to simplify node enrollment.
This patch also deprecates `ansible_deploy_username` and
`ansible_deploy_key_file` options in node's driver_info in favor of
`ansible_username` and `ansible_key_file` respectively.
Change-Id: Ib198c07c1d414c0d78950e5d98a5176e12a7df13
Closes-Bug: #1736409
ce7119eaf3