* Add ability to read and list hosts. Tests to follow.
* Add tests for reading and listing as well as validation checks to not modify hosts.
* Add IpAddress and DnsNames to the api resource. Populate the plugin info.
* Adding go sdk tests for reading and listing hosts and ensuring update and deleting is disallowed.
* Remove Prefix Id and Plugin Name fields. Creating catalogs now require either the plugin id or the name of the plugin resource (but not both). Host Catalogs and Host Sets API resources now have a read only plugin field populated with plugin info. Host Catalogs have a plugin id field as a top level field.
This moves the generated pb files to the `sdk` module. This allows third parties to make use of them if desired (e.g. in upcoming plugins) and moves away from the `gen` nomenclature in the directory, since we are going to be adding some extra interface functions to the messages.
Jeff Mitchell
Todd