This way, error lines like this one:
Waiting for emulator to start: unknown: error: no devices found
Become:
Waiting for emulator to start: error: no devices found
Otherwise, we'd interpret this as "booting", which is wrong:
$ adb -e shell getprop init.svc.bootanim
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
error: no devices found