Adds additional thrown exception or 401 unauthorized.

[johnbburg]

Fixes #1097

• Adds additional thrown exception or 401 unauthorized.
• Backports convertBodyToString method.
• Handles responses with empty bodies.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[ezimuel]

Closing this since it's outdated. Not supporting anymore 6.x, sorry.