Final metrics option integration

Depends on https://github.com/strongloop/strong-statsd/pull/11
not the first time, maybe. first time is probably either in sl-run.js, where .profile() is called, though that call is not made if --no-profile is specified. in which case, the next place agent could be required is in metrics setup, assumming --metrics is set, or there is a parent process, when .use() is called, triggering agent.start(). but if all those calls don't happen... then this is the first. and it doesn't matter that its happening after the fact, because if there is no strongops and no metrics, none of the agent features that require early monkey-patching are going to be used.

So, no, I don't think its a problem.

Also, this code is in master, so the app isn't loaded at all, if you mean the user's app.