change how pythonpath is updated

Dockerfile

@@ -9,10 +9,9 @@ RUN pip install --upgrade pip
 RUN pip install PyYAML google-auth-httplib2 google-api-python-client gcs-oauth2-boto-plugin \ 
 retrying firecloud xlrd google-cloud-bigquery google-cloud-logging pandas
 
-RUN export PYTHONPATH=./:$PYTHONPATH
-
 # Tell gcloud to save state in /.config so it's easy to override as a mounted volume.
 ENV HOME=/
 
 COPY scripts /scripts
 CMD ["/bin/bash"]
+ENV PYTHONPATH="/scripts"