virttest.qemu_devices: Use the bus function to check if it matches the spec

When we try to match a bus to some specification (dictionary) it makes
sense to ask the bus and not to try to guess. This way we can customize
the function to each bus, if necessarily.

Additionally make it possible to ignore autotest type by setting
atest=False. This could be used to see if this specification matches from
qemu point of view, but doesn't match from autotest point of view.
(from qemu point of view ahci and ide bus is the same, but in autotest
we want to make sure the ide-hd goes into the correct HBA). This feature
will be used in the following patch.

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