Address unit test failures

A number of failures were observed,
* GPlay dev license server is being worked on. This causes random
  failures when running unit tests. Switching to the staging
  server for now.
* Occasionally, the license server times out. Introducing a retry
  mechanism do deal with HTTP responses (merge from master #45e8ddd5f)
* Release license tests are now disabled. Tests were previously passing,
  even though they were not in fact supported by the GPlay license server.
  The response included just enough information to be a valid license and
  passed minimal verification that was taking place. Additional verification
  was not necessary because session is torndown and resources released as
  soon as the response has been received.
  A change at the GPlay server now causes the release license request to be
  flagged as an error and the tests to fail. Work is in progress to
  support release of licenses at the GPlay server.
* The wrong message test (from request license tests) fails. This is
  because GPlay behaviour changed from returning a HTTP 500, when
  processing an invalid PSSH, to returning a HTTP 200 without any included
  license.
* Security level path backward compatibility tests on L3 which failed and
  caused the succeeding license request tests to fail.

b/12000457

Change-Id: I8e6adc490504475d1039793ea555a17799cb78c4

libwvdrmengine/test/java/src/com/widevine/test/MediaDrmAPITest.java

@@ -73,7 +73,7 @@ class SurfacePanel extends SurfaceView implements SurfaceHolder.Callback
 public class MediaDrmAPITest extends Activity {
     private final String TAG = "MediaDrmAPITest";
 
-    static final String kKeyServerUrl = "https://jmt17.google.com/video-dev/license/GetCencLicense";
+    static final String kKeyServerUrl = "https://jmt17.google.com/video/license/GetCencLicense";
     static final String kOperatorSessionKeyServerUrl = "http://kir03wwwg185.widevine.net/drm";
 
     static final UUID kWidevineScheme = new UUID(0xEDEF8BA979D64ACEL, 0xA3C827DCD51D21EDL);