Allow crowbar commands to handle multiple positional arguments.

This also adds back some basic help, and fixes up the error
handling paths in the application controller to return json-wrapped
errors if we are talking JSON.
Merge pull request #810 from VictorLowther/pull-req-master-dd62f62a06f9c85d18f343d9bfb729401e65b330

https://github.com/crowbar/barclamp-crowbar/pull/810

Merged by devtool for VictorLowther