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_prctl_test.cpp b/tests/sys_prctl_test.cpp
index cd23c0a..6d1fa1d 100644
--- a/tests/sys_prctl_test.cpp
+++ b/tests/sys_prctl_test.cpp
@@ -61,7 +61,7 @@
 
   ASSERT_EQ(0, munmap(p, page_size * 3));
 #else
-  GTEST_LOG_(INFO) << "This test does nothing as it tests an Android specific kernel feature.";
+  GTEST_SKIP() << "PR_SET_VMA not available";
 #endif
 }
 
@@ -112,7 +112,6 @@
   EXPECT_EQ(-1, err);
   EXPECT_EQ(EINVAL, errno);
 #else
-  GTEST_LOG_(INFO)
-      << "Skipping test that requires host support for PR_CAP_AMBIENT.";
+  GTEST_SKIP() << "PR_CAP_AMBIENT not available";
 #endif
 }