The generic approach of calling avrdude to perform a reset with `make reset`
does also work on board with a bootloader, but only if no other process is
also accessing the serial (e.g. via `make term`). `make test` first accesses
the serial and then performs `make reset` to not miss any output on the serial.
This however blocks when `make reset` also wants to access that serial.
As workaround, `make reset` is no only provided if the ATmega device is not
programmed via bootloader. Normally, those boards reset anyway upon `make term`,
which allows `make test` to work normally again.
f44dd00276