JVM heap size is not set correctly for Java actions

@rabbah commented on [Thu Jun 15 2017](https://github.com/apache/incubator-openwhisk/issues/2389)

Java actions run with no heap settings, regardless of the container's memory limit: https://github.com/apache/incubator-openwhisk/blob/master/core/javaAction/Dockerfile#L38

This will cause a reused Java action to eventually be killed because the GC may not get a chance to run.

```bash
> docker run -m 64M -it javaaction bash
# java -XX:+PrintFlagsFinal -version 2>&1 | grep MaxHeapSize
uintx MaxHeapSize := 1035993088 {product}
```

That's ~1GB even though memory limit for container is 64M.

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@jsanda commented on [Mon Oct 23 2017](https://github.com/apache/incubator-openwhisk/issues/2389#issuecomment-338742448)

Is something like [this](https://github.com/fabric8io-images/java/tree/master/images/jboss/openjdk8/jdk) what you have in mind? run-java.sh is the default command for the image. Among other things it sets the JVM heap size based on container limits.