CLI wsk api get to generate API consumer friendly swagger file

@csantanapr commented on [Thu Apr 27 2017](https://github.com/apache/incubator-openwhisk/issues/2198)

The WSK CLI would need to be adjust , today by default the support export admin cfg file, and import the same admin cfg, it's not a swagger file for consumers.

The WSK CLI would need to be updated with a flag to indicate that the desire output is for consumers of the API (ie wsk api get --consumer > consumer_client_swagger.json)

The file will be ready to be use as it will have the full basePath and host client can use to call the APIs.
The full basePath and host (i.e. 172.17.0.1:9001) that a consumer API consumer would use say with `curl` will be constructed from the managedUrl value we get back from API Gateway management interface.