This is a follow-up to commit 350aeaff66.
1. Change the default driver for new nodes to pxe_ipmitool as it's our
go-to default driver.
2. Add a release note with a link to more details.
Change-Id: I3535cbfbffd2ce394b4e828c53a7fba6ee46fb5c
Implements: blueprint inspector-node-autodiscovery