Get the automated tests up and running again

* Fix the build.gradle file
* Use the correct VisibleForTesting class
* Fix the Android test setUp() logic
* Enable a test in DeliveryReceiptJobTest.java where the @Test anotation was missing

It should be noted that the tests in AttachmentDatabaseTest.java fail.

Fixes #3474
Closes #5882

test/androidTest/java/org/thoughtcrime/securesms/TextSecureTestCase.java

@@ -6,7 +6,7 @@ import android.test.InstrumentationTestCase;
 public class TextSecureTestCase extends InstrumentationTestCase {
 
   @Override
-  public void setUp() throws Exception {
+  public void setUp() {
     System.setProperty("dexmaker.dexcache", getInstrumentation().getTargetContext().getCacheDir().getPath());
   }