Block other processes when bubbler is on

[je-foster]

We make a great effort to keep the TankController loop time short. This is good design, allowing the device to maintain critical functions while it makes slower progress on less-urgent tasks. The most critical function that is especially vulnerable to delay is the CO2 bubbler, and we give it special attention: We decided to postpone ethernet processes whenever the bubbler is active because the ethernet library has a 1-second delay when establishing a network connection. There may be other processes that should also not run while the bubbler is active.

If the CO2 bubbler is our highest priority whenever it is active, and if its duration is always to be for less than 1 second, perhaps it would be safest and easiest to make the bubbler a blocking process.