qemu: capabilities: Always assume QEMU_CAPS_BOOTINDEX

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: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

tests/qemuxml2argvdata/aarch64-gic-v2.args

@@ -20,5 +20,4 @@ path=/tmp/lib/domain--1-aarch64test/monitor.sock,server,nowait \
 -mon chardev=charmonitor,id=monitor,mode=control \
 -rtc base=utc \
 -no-shutdown \
--no-acpi \
--boot c
+-no-acpi