STORM-188: Allow user to specifiy full configuration path when running storm command

We can use system config "storm.conf.file" to specify a custom config file.

Before this patch, we will only try to lookup this file on jvm classpath.

This patch will give us the ability to specify full/relative filesystem path as configuration file path, thus will give us more flexibility, while we still are able to look it up on jvm classpath.

Now we are able to submit storm topology like this: 

```bash
storm jar job.jar --config /tmp/dynamic-configuration-path.yaml
```

We don't need to add /tmp into our classpath(also inappropriate).
It might be nice to log something here, so that the user knows that we are using a config file from the classpath.  I just thought about the case where someone creates a ./storm.yaml file and passes it in with --config.  They will get the storm.yaml from the classpath without knowing it, because the classpath is searched prior to the absolute path being searched, and this would be really confusing.