The field was added in qemu v0.13.0-rc0-731-g1ca4d09ae0 so all supported
qemu versions now use it.

There's a LOT of test fallout as we did not use capabilities close
enough to upstream for many of our tests.

Several tests had a 'bootindex' variant. Since they'd become redundant
they are also removed here.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>