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/pty_test.cpp b/tests/pty_test.cpp
index 75f228c..29f86f1 100644
--- a/tests/pty_test.cpp
+++ b/tests/pty_test.cpp
@@ -109,8 +109,7 @@
   cpu_set_t cpus;
   ASSERT_EQ(0, sched_getaffinity(0, sizeof(cpu_set_t), &cpus));
   if (CPU_COUNT(&cpus) < 2) {
-    GTEST_LOG_(INFO) << "This test tests bug happens only on multiprocessors.";
-    return;
+    GTEST_SKIP() << "This bug only happens on multiprocessors";
   }
   constexpr uint32_t TEST_DATA_COUNT = 2000000;