Include googletest cmake support.

- Same googletest release (v1.8.0), new root in third_party.
- Update Android.mk and make build (include and file locations).
- Update cmake build (use googletest's cmake support).
- Update gtest include in all tests.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=76

Change-Id: I5491a2ff3c8869263cd885872c815402236c20b1
diff --git a/test/util.h b/test/util.h
index f63fda1..a20fab6 100644
--- a/test/util.h
+++ b/test/util.h
@@ -14,7 +14,7 @@
 
 #include <stdio.h>
 #include <math.h>
-#include "third_party/googletest/src/include/gtest/gtest.h"
+#include "third_party/googletest/src/googletest/include/gtest/gtest.h"
 #include "aom/aom_image.h"
 
 // Macros