[Fix JENKINS-16632] Don't print auth stack traces.

Really fix JENKINS-16632. We cannot print the AuthorizationException
stack trace because it contains private auth info and printing the stack
trace writes it to the Jenkins build console log. Instead catch
AuthorizationExceptions then create a new RuntimeException whose message
can be printed. Print the RuntimeException stack trace and a helpful
message that authorization failed.
Merge pull request #36 from cboylan/fix-JENKINS-16632

[Fix JENKINS-16632] Don't print auth stack traces.