ART: Allow scoped adjustments to log verbosity

Add ScopedLogSeverity to adjust the logging level.

Suppress warnings by default in gtests. Suppress errors in instances
where errors are expected.

Change-Id: If3ef865813e9505ab60bc90baed63ff11d90afbb
diff --git a/runtime/utils_test.cc b/runtime/utils_test.cc
index a98bc90..a3dd13c 100644
--- a/runtime/utils_test.cc
+++ b/runtime/utils_test.cc
@@ -392,6 +392,9 @@
 }
 
 TEST_F(UtilsTest, ExecError) {
+  // This will lead to error messages in the log.
+  ScopedLogSeverity sls(LogSeverity::FATAL);
+
   std::vector<std::string> command;
   command.push_back("bogus");
   std::string error_msg;