Make health checks more frequent in Docker

5 min was copy/paste from official docs. After reading more about health
checks in real world usage most examples was using duration around
5 seconds for interval. By default docker will show if service is
unhealthy after 3 intervals return error. So in previous timing service
would be taken out of poll (by e.g. docker swarm) after 15 min. For all
this time it would be returning errors for any communication to it. Now
it will be removed from poll of running services after 15 seconds.

Regarding timeout more examples was using something shorter. For all
services we are using if anything respond longer than 2 seconds then
something is wrong with this service. Monasca is not web service but
back-end service that should have high throughput.

Change-Id: I4486c4974de38dea33739fdc470f38fd99d428fa

docker/Dockerfile

@@ -129,7 +129,7 @@ ONBUILD RUN \
                     -o \( -type f -a \( -name '*.pyc' -o -name '*.pyo' \) \) \
                 \) -exec rm -rf '{}' +
 
-ONBUILD HEALTHCHECK --interval=5m --timeout=3s \
+ONBUILD HEALTHCHECK --interval=5s --timeout=2s \
                    CMD python3 health_check.py || exit 1
 
 ENTRYPOINT ["/sbin/tini", "-s", "--"]

docker/README.rst

@@ -33,7 +33,8 @@ start.sh
 
 health_check.py
   This file will be used for checking the status of the application running in
-  the container. It will be useful for container orchestration like Kubernetes
+  the container. It should be used to inform Docker that service is operating
+  and healthy. It will be useful for container orchestration like Kubernetes
   or Docker Swarm to properly handle services that are still running but
   stopped being responsive. Avoid using `curl` directly and instead, use
   `health_check.py` written with specific service in mind. It will provide more