qemu.tests.pci_devices: Add test of pci devices

This test boots VM with a define set of PCI devices and compares
the qtree and internal representation.

In the future this test should also check the operation system view
of the devices (lspci or the windows equivalent)

The testing setup is done via graphical representation of the setup.
Note that the number of spaces is irelevant. The location is defined
by the number of '->' characters. You can verify the setup in the test.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
virttest.qemu_devices_unittest.py: Update unittest to suit the changes

There were lot's of changes so please accept this single unittest
update instead of incremental one.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
virttest.qemu_devices: Fix missing IDE bus for CDROM

Default CDROM is ide. Change this to AHCI in case VM doesn't have
IDE bus.

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