allow drifts using engineering fibers

After looking at the distribution of available fiber bundles, we know that we need to take drift flats with the engineering fibers. I gave that a try with `iic drift --iisHalogen ....`. That seemed to need a change to one of the `sps` -> `enu` commands (`iic halogen` -> `iic prepare halogen`). The lamps then behaved, but the `slit linearVerticalMove` command was not being sent and I ran out of time to look further.