Add test for RefBase etc.

Add some basic tests for RefBase, as well as a more ambitious memory
ordering test.

Add a README.txt with instructions to run the tests.

Comment out a couple of BlobCache tests that failed consistently and
appeared to be incorrect.  With that fix, I managed to run
libutils_tests successfully on device.

Bug: 28705989
Change-Id: I8ad29995097a149a0cc38615d6ed37117ec6cb5c
diff --git a/libutils/tests/README.txt b/libutils/tests/README.txt
new file mode 100644
index 0000000..ad54e57
--- /dev/null
+++ b/libutils/tests/README.txt
@@ -0,0 +1,8 @@
+Run device tests:
+
+mma -j<whatever>
+(after adb root; adb disable-verity; adb reboot)
+adb root
+adb remount
+adb sync
+adb shell /data/nativetest/libutils_tests/libutils_tests