Add mechanism to lie about the camera name

The ics_xcu_fpga CCD object accepts an optional override for the camera name. This is used by IDG test scripts running in the optics lab, where the piepan is always r9 but the tested detectors change (from r1 to b1, say).

The ccdActor needs to grow the ability to know how and when to override the camera id. A config option is the sensible mechanism. The only trick is that it needs to get the override before it completely instantiates the actor.