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/time_test.cpp b/tests/time_test.cpp
index 50830ee..637fa85 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -912,6 +912,6 @@
   ASSERT_EQ(0, timespec_get(&ts, 123));
   ASSERT_EQ(TIME_UTC, timespec_get(&ts, TIME_UTC));
 #else
-  GTEST_LOG_(INFO) << "glibc doesn't have timespec_get until 2.21\n";
+  GTEST_SKIP() << "glibc doesn't have timespec_get until 2.21";
 #endif
 }