Increase default runtest -j to 16.

Change-Id: I4f98a630a7ad75557e462a122b83dd3c36cf6ab6
diff --git a/testrunner/runtest.py b/testrunner/runtest.py
index 6226350..56e847b 100755
--- a/testrunner/runtest.py
+++ b/testrunner/runtest.py
@@ -69,7 +69,7 @@
       "for a list of tests, or you can launch one or more tests.")
 
   # default value for make -jX
-  _DEFAULT_JOBS = 4
+  _DEFAULT_JOBS = 16
 
   _DALVIK_VERIFIER_OFF_PROP = "dalvik.vm.dexopt-flags = v=n"