qemu: implement setting of rotation rate for SCSI/IDE disks

qemu: implement setting of rotation rate for SCSI/IDE disks

This is available in QEMU with "ide-hd" and "scsi-hd" device
types. It was originally mistakenly added to the "scsi-block"
device type too, but later removed. This doesn't affect libvirt
since we restrict usage to device=disk.

When this property is not set then QEMU's default behaviour
is to not report any rotation rate information, which
causes most guest OS to assume rotational storage.

https://bugzilla.redhat.com/show_bug.cgi?id=1498955

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>