virttest.qemu_devices: Use qid for hotplug verification

Proper identification in qemu_devices is object.get_qid().

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
qemu.tests.virtio_console: Update test_hotplug_virtio_pci

Fix the problem with duplicated IDs caused by early device_del execution.
Monitor returns no output but internally waits for OS ACPI respone. This
message, in case kernel is not yet initialized, never occurs.

This version resends the device_del in the first round until it succeeds,
than it just waits until the device disappears.

Additionally the test was rewritten to use qemu_devices to handle the
hotplug/unplug and the test cfg was tweaked to be more intensive.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Merge pull request #1206 from ldoktor/virtio_console

qemu.tests.virtio_console: Update test_hotplug_virtio_pci