Use new hashing of static file names.

Every time the docker image is rebuilt a random hash is chosen.

Requires Pillar d560f89704e3a6f4490df57712525048c469bed2 or newer.

docker/4_run/Dockerfile

@@ -56,3 +56,7 @@ ENTRYPOINT /docker-entrypoint.sh
 # Add the most-changing files as last step for faster rebuilds.
 ADD config_local.py /data/git/blender-cloud/
 ADD deploy /data/git
+RUN python3 -c "import re, secrets; \
+f = open('/data/git/blender-cloud/config_local.py', 'a'); \
+h = re.sub(r'[_.~-]', '', secrets.token_urlsafe())[:8]; \
+print(f'STATIC_FILE_HASH = {h!r}', file=f)"