virttest.qemu_devices: Skip 'driver=' string in devices

Libvirt doesn't use the full cmdline, but only -device $driver,$params
format. This patch makes autotest follow this syntax too.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
shared.cfg.machines: Disallow 'ide' usage on q35

q35 doesn't have ide bus. People should use ahci instead.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
virttest.qemu_vm: Remove unused functions add_drive and add_cdrom

add_drive and add_cdrom are obsoleted by
virttest.qemu_devices.images_define_by_variables()

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