tests: Add default-models cases for many architectures

tests: Add default-models cases for many architectures

These are similar to the minimal cases that we just introduced,
but are intended to demonstrate what device or controller model
libvirt will choose when one is not provided by the user.

Note that we want both regular and ABI_UPDATE variants of the
various test cases because, in some cases, the behavior for new
guests is not the same as that for existing ones due to backward
compatibility concerns.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>