Ironic code now provide PXE configuration tools. So we can drop our own
PXE related code.
Ironic images manipulation code have been improved. This allow to drop
some more our code.
Change-Id: Iaeda025456dbde9163c792e6de6d165c6f03f197
Use deployment-config validation API provided by bareon's data-drivers. It
makes early deployment termination possible in case of an error in
deployment-config.
Change-Id: I17b5d74f1452c9bb2ae3ea63ab0ee8f1fe597ae9