Java SDK should support the Gov auth model

[cleemullins]

This C# PR needs to be migrated to Java:
(Luis Regions) microsoft/botbuilder-dotnet#1077
(Auth endpoints) microsoft/botbuilder-dotnet#890

[tracyboehrer]

Preview 2 notes:

This was tested on Gov Azure using the servlet sample. The sample includes ARM templates to properly deploy the sample to Gov. The directions in Readme.md should be adjusted to use either template-with-new-rg-gov.json or template-with-preexisting-rg-gov.json.