os: Add q35/ich9/e1000e to rhel6

rhel6 does support q35, it just has some issues when combined with
virtio, as rhel6 doesn't support virtio1.0

https://ladipro.wordpress.com/2016/10/17/virtio1-0-and-windows-guests/



However that decision should be left up to apps and not mandated by
osinfo metadata.

Add this annotation for rhel6 to ensure apps aren't naively depending
solely on the presence of qemu-x86-q35 in the device list, and instead
checking for specific virtio support as well

Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>