tests/device-plug: Add memory unplug request test for spapr

tests/device-plug: Add memory unplug request test for spapr

We can easily test this, just like PCI. On x86 ACPI, we need guest
interaction to make it work, so it is not that easy to test. We might
add tests for that later on.

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190218092202.26683-7-david@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>