[refactoring] stop using pxe_ssh as the default drivers in tests
[refactoring] stop using pxe_ssh as the default drivers in tests

This driver is going away, and we no longer support it in instack-undercloud.
Let's use the more realistic 'ipmi' driver instead as an example.

Change-Id: Ia5a1de1e85b38766da849957397fa87c7db01b45

openstack/tripleo-common,openstack/tripleo-common