Make run-core-tests with no arguments equivalent to tests.AllTests.

Previous behavior would run the same set of tests, but without going through
the regular pre- and post-processing, and without initializing the command-line
flags to their default values.
diff --git a/luni/src/test/java/com/google/coretests/Main.java b/luni/src/test/java/com/google/coretests/Main.java
index 1dcebc5..4a91a95 100644
--- a/luni/src/test/java/com/google/coretests/Main.java
+++ b/luni/src/test/java/com/google/coretests/Main.java
@@ -27,7 +27,7 @@
     public static void main(String[] args) {
         if (args.length == 0) {
             System.out.println("Running all tests...");
-            TestRunner.run(AllTests.suite());
+            CoreTestRunner.main(new String[] { "tests.AllTests" });
         } else if ("--stats".equals(args[0])) {
             // Delegate to new stats test runner
             String[] args2 = new String[args.length - 1];