bionic tests: use GTEST_SKIP.

Also be a bit more to the point in our messages, focusing on "why" not
"what".

Test: ran tests
Change-Id: I297806c7a102bd52602dcd2fcf7a2cd34aba3a11
diff --git a/tests/sys_stat_test.cpp b/tests/sys_stat_test.cpp
index 70ad451..97bf580 100644
--- a/tests/sys_stat_test.cpp
+++ b/tests/sys_stat_test.cpp
@@ -82,7 +82,7 @@
     unlink(path.c_str());
   } else {
     // SELinux policy forbids us from creating FIFOs. http://b/17646702.
-    GTEST_LOG_(INFO) << "This test only performs a test when run as root.";
+    GTEST_SKIP() << "SELinux policy forbids non-root from creating FIFOs";
   }
 }