[Test] use parallelism in quicktest by default

docker/quicktest.sh

 #!/bin/bash
 
+: ${PYTEST_PARALLEL=auto}
+
 cd $FINN_ROOT
-python setup.py test --addopts "-m 'not (vivado or slow)'"
+python setup.py test --addopts "-m 'not (vivado or slow)' --dist=loadfile -n $PYTEST_PARALLEL"