The 'ironic' CLI is going to be deprecated [1]; the 'openstack baremetal'
(OSC) CLI should be used instead. This changes the documentation to refer
to the OSC CLI.
[1] https://bugs.launchpad.net/python-ironicclient/+bug/1700815
Change-Id: I737ba38c6130e7ba123368b6081c4923d1423d98