Add utility for streaming command output to logger

[bluekeyes]

The current method looks something like this:

CommandFuture future = Commands.executeAsync(cmd);
ResponseProvider<Runnable> responses = UnorderedResponseProvider.<Runnable>builder()
        .addRegex(".*", new Function<String, Runnable> () {
            @Override
            public Runnable apply(final String input) {
                return new Runnable() {
                    @Override
                    public void run() {
                        logger.info(input);
                    }
                };
            }
        })
        .build();
CommandOutputTrigger outputTrigger = new CommandOutputTrigger(responses, future);
outputTrigger.start();
Commands.waitFor(future);

Since this is a relatively common pattern, there should be a utility that simplifies this.

[bluekeyes]

Make sure this can stream from either stdout, stderr, or the combination of both.