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/dlext_test.cpp b/tests/dlext_test.cpp
index cace36c..aa65a53 100644
--- a/tests/dlext_test.cpp
+++ b/tests/dlext_test.cpp
@@ -540,10 +540,7 @@
 }
 
 TEST_F(DlExtRelroSharingTest, VerifyMemorySaving) {
-  if (geteuid() != 0) {
-    GTEST_LOG_(INFO) << "This test must be run as root.\n";
-    return;
-  }
+  if (geteuid() != 0) GTEST_SKIP() << "This test must be run as root";
 
   TemporaryFile tf; // Use tf to get an unique filename.
   ASSERT_NOERROR(close(tf.fd));