[test_util] ASSERT_OK should work outside kudu ns

This patch makes ASSERT_OK work when called from outside the Kudu
namespace by replacing bare const Status& with const auto&.
(::kudu::Status would have also worked but auto is already used here)

src/kudu/util/test_macros.h

@@ -30,7 +30,7 @@
   if (testing::Test::HasFatalFailure()) { return; }
 
 #define ASSERT_OK(status) do { \
-  const Status& _s = status;        \
+  const auto& _s = status;        \
   if (_s.ok()) { \
     SUCCEED(); \
   } else { \
@@ -39,7 +39,7 @@
 } while (0);
 
 #define EXPECT_OK(status) do { \
-  const Status& _s = status; \
+  const auto& _s = status; \
   if (_s.ok()) { \
     SUCCEED(); \
   } else { \
@@ -50,7 +50,7 @@
 // Like the above, but doesn't record successful
 // tests.
 #define ASSERT_OK_FAST(status) do { \
-  const Status& _s = status; \
+  const auto& _s = status; \
   if (!_s.ok()) { \
     FAIL() << "Bad status: " << _s.ToString(); \
   } \