Fix for localhost metrics manager

[jrcrawfo]

What?

• Fixes for getting local hostname from within a Docker container

Why?

• Metrics management doesn't work correctly if running Heron using Docker containers deployed in a cluster environment

[maosongfu]

Two comments:

1. Do you think we could make:

 if (System.getenv("HOST") != null) {
        this.hostname = System.getenv("HOST");
     } else {
        this.hostname = InetAddress.getLocalHost().getHostName();
     }

as an utlity method rather than duplicate the code multiple times?

2. Use a more specific system env name like HERON_SERVER_HOST rather than the generic HOST to avoid any unexpected system injection?

[jrcrawfo]

#1. Yes, we should do that. I’ll make that change.

#2. The reason for using HOST is because it is commonly passed in by the scheduler to be an actual resolvable hostname in a Docker environment (where hostname otherwise is the container id). So, it’s best to leave this as is, as there is also a helper function in the python executor code to do the same logic.

[maosongfu]

@jrcrawfo
Fair. Will give a ship it once:

1. The utility method is added.
2. The Travis Ci build can pass.

[kramasamy]

@jrcrawfo - any update on this PR?

[nlu90]

@jrcrawfo Ping for this PR, any updates?