Add a quick status utilility

@cfjedimaster commented on [Mon Oct 23 2017](https://github.com/apache/incubator-openwhisk/issues/2886)

It would be nice if there was a quick way to get stats about an action. So something like:

wsk stats ACTIONNAME

Which would report a very brief summary:

ACTIONNAME has had X invocations in 24h. Average duration is 219ms. Error rate is 2%

Obviously Bluemix's online reporting can show some of this and you can build your own tools to report similar values, but I'm thinking that the CLI could provide a quick summary of your action and that could be pretty useful.