Optimizations/restructuring from profiling

The BeagleBone Black's processor maxes out:
* when both buses are full rate
* when one bus is full rate and Bluetooth is connected
Added more testing tools

* `can_stress` puts full load on CAN bus(es)
* `isoblue_dummy` replaces Android library in testing
Fixed bottleneck responsible for problem in 828b6b160d09cb427c48a54279d9f8821d1c5e2d