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/system_properties_test2.cpp b/tests/system_properties_test2.cpp
index e6e7ef2..c061faa 100644
--- a/tests/system_properties_test2.cpp
+++ b/tests/system_properties_test2.cpp
@@ -124,7 +124,7 @@
     ASSERT_EQ(expected_name, legacy_name);
     ASSERT_STREQ("value2", propvalue);
 #else // __BIONIC__
-    GTEST_LOG_(INFO) << "This test does nothing.\n";
+    GTEST_SKIP() << "bionic-only test";
 #endif // __BIONIC__
 }
 
@@ -143,6 +143,6 @@
     }
 
 #else // __BIONIC__
-    GTEST_LOG_(INFO) << "This test does nothing.\n";
+    GTEST_SKIP() << "bionic-only test";
 #endif // __BIONIC__
 }