439507 - Possible timing side-channel when comparing MD5-Credentials

+ Using correct digestMismatch logic
+ Fixing test cases:
  + No longer reuses / shares directories
  + Is now Windows build/test compatible
  + No longer deleteOnExit() the test data
    (let maven clean and/or test init do that)
  + Empty directories are now verified
  + Using server.getURI() instead of URL string manipulation