Clarify Dome Simulator Code

[wtgee]

There is a whole lot of code that is set up for a dome simulator and it is not at all clear how it works or what it is supposed to be doing. There is also a mix of testing items (e.g. pocs.tests.serial_handlers) that are being used within the main module (e.g. pocs.dome.protocol_astrohaven_simulator). Again, it's not at all clear how any of this interacts.

In adding documentation as part of #635 I'm changing a bit of how test discovery works and this is leading to errors that are difficult to trace (such as where NoOpSerial comes from - #637 )