virttest.qemu_devices: Differentiate between qemu and autotest bus type

qemu doesn't differentiate between some of the buses, which are
differentiated in autotest (eg. ahci and ide disks belongs simply
to IDE bus type). In order to be able to distinguish between those
buses we need to add atype (=autotest type) of the bus.

This patch makes this change only for images, where were problems
caused by different qemu/autotest behavior. If this concept prooves
to be right, we can use it to distinguish between various kinds of
USBs in order to reflect the qemu behavior while keeping the autotest
standards.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>