KVM Test: Add change_media new test script.

This script cover following tcms test cases:
[QMP] change removable media
[QMP] change a removable media with media&locked in drive with change
[QMP] Change a non-removable media with change

This script also work with human monitor.

Signed-off-by: Feng Yang <fyang@redhat.com>
Acked-by: Amos Kong <akong@redhat.com>
Acked-by: Qingtang Zhou <qzhou@redhat.com>
config: Add config used in virt_test_utils.get_readable_cdroms()

Signed-off-by: Feng Yang <fyang@redhat.com>