qemu-iotests, qtest: rewrite test 067 as a qtest

qemu-iotests, qtest: rewrite test 067 as a qtest

Test 067 from qemu-iotests is executing QMP commands to hotplug
and hot-unplug disks, devices and blockdevs.  Because the power
of the text-based test harness is limited, it is actually limiting
the checks that it does, for example by skipping DEVICE_DELETED
events.

tests/qtest already has a similar test, drive_del-test.c.
We can merge them, and even reuse some of the existing code in
drive_del-test.c.  This will improve the quality of the test by
covering DEVICE_DELETED events and testing multiple architectures
(therefore covering multiple PCI hotplug mechanisms as well as s390x
virtio-ccw).

The only difference is that the new test will always use null-co:// for
the medium rather than qcow2 or raw, but this should be irrelevant for
what the test is covering.  For example there are no "qemu-img check"
runs in 067 that would check that the file is properly closed.

The new tests requires PCI hot-plug support, so drive_del-test
is moved from qemu-system-ppc to qemu-system-ppc64.

Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>