Curator updates.

- Update Python to 3.7.
- Update Curator to 5.5.4.
- Fix crontab issue.

curator/.dockerignore

 *
+!entrypoint

curator/Dockerfile

-FROM python:3.6-alpine
-RUN pip install --no-cache-dir elasticsearch-curator==5.4.1
-CMD /usr/sbin/crond -f
+FROM python:3.7-alpine
+RUN pip install --progress-bar=off --no-cache-dir elasticsearch-curator==5.5.4
+COPY --chown=root:root entrypoint /
+ENTRYPOINT [ "/entrypoint" ]
+CMD [ "/usr/sbin/crond", "-fd7" ]
 HEALTHCHECK --timeout=1s CMD pgrep crond || exit 1

curator/entrypoint

+#!/bin/sh
+set -eu
+
+crontab -u nobody /etc/crontabs/nobody
+eval exec "$@"