Make Swagger API support optional, so that consumers can define their own

OpenShift would like to also enable swagger, but we need to register our
services as swagger services prior to the SwaggerAPI being started. I've
added a bool (default false) to master.Config to enable swagger, and split
the method in master out so that a downstream consumer can call it.
ubuntu getting started guide
Merge pull request #2945 from smarterclayton/support_optional_swagger

Make Swagger API support optional, so that consumers can define their own
Merge pull request #2857 from jainvipin/master

ubuntu getting started guide