Add Ironic support to incubator.

This patch:

 - adds metadata for Ironic to testenv's.
 - adds a variable (USE_IRONIC) which controls whether to use Ironic
   or Nova-BM in baremetal clouds.
 - implements cloud bringup logic for Ironic.

Co-Authored-By: Gregory Haynes <greg@greghaynes.net>
Co-Authored-By: Devananda van der Veen <devananda.vdv@gmail.com>
Co-Authored-By: Robert Collins <rbtcollins@hp.com>
Change-Id: Ib80fa745ccd9ef54e7582d8e86fdbc49230ee616
Merge "Add Ironic support to incubator."