run_unittests returns a proper exit status.

It'll now return 0, 1 or 2, corresponding to the number of test
invocations (either user or root privileged) that failed.

BUG=None
TEST=Script runs and returns correct status.

Change-Id: I0d5bd8436b1a9972337f34073321239d94565748
Reviewed-on: https://gerrit.chromium.org/gerrit/31006
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Ready: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>

run_unittests

diff --git a/run_unittests b/run_unittests
index 2bafab4..7a7c85a 100755
--- a/run_unittests
+++ b/run_unittests
@@ -19,3 +19,5 @@
 
 echo -n "User tests: " && [ $user_pass == 1 ] && echo "PASSED" || echo "FAILED"
 echo -n "Root tests: " && [ $root_pass == 1 ] && echo "PASSED" || echo "FAILED"
+
+exit $((2 - user_pass - root_pass))