qemuxml2argvtest: Use real-caps testing for 'acpi-hotplug-bridge-disable'

qemuxml2argvtest: Use real-caps testing for 'acpi-hotplug-bridge-disable'

We can use real example configs to prove the support without the
need for using fake capabilities. Fix the recently added test cases.

The negative case for 'pc-i440fx-acpi-hotplug-bridge-disable' is removed
completely as there is no real qemu libvirt supports which wouldn't
have the capability.

The input file for the negative test on aarch64 is modified so that it's
actually a reasonably valid VM config.

Fixes: bef0f0d8be6
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>