tests/acpi: unit test for 'acpi-pci-hotplug-with-bridge-support' bridge flag

tests/acpi: unit test for 'acpi-pci-hotplug-with-bridge-support' bridge flag

This change adds a new unit test for the global flag
'acpi-pci-hotplug-with-bridge-support' which is available for cold plugged pci
bridges in i440fx. The flag can be used to turn off ACPI based hotplug support
on all pci bridges.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200918084111.15339-8-ani@anisinha.ca>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>