virttest.qemu_devices: Make IDE bus strict_mode only

When using IDE bus, only ide.1 bus is used by default. We have to
force the ide.0 in order to use it (similar to AHCI). This patch
makes all QBusUnitBuses act this way.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Merge pull request #1045 from ldoktor/add_device3

virttest.qemu_devices: Make IDE bus strict_mode only