As of recently, deploy images for overcloud nodes may now be file-based
rather than in Glance. And after upcoming changes to Ironic,
driver_info.deploy_kernel and driver_info.deploy_ramdisk may be empty.
With the need to be both forwards- and backwards-compatible, the
validation logic here has been necessarily loosened: merely checking
that nodes of the same arch/platform do not have overly diverse deploy
images associated. Such validation is not as entirely definitive or
detailed as its predecessor, but also far less convoluted than any
alternative...
Change-Id: I5aa4e98770f29cd2df3f39e4000b822681c551f4
b488ec9c81