Suppress expected exceptions by report_on_exception = false

This suppresses `Timeout::Error` exceptions.
Ref: https://travis-ci.org/rails/rails/jobs/334622442#L1089-L1110

activesupport/test/cache/behaviors/connection_pool_behavior.rb

@@ -2,6 +2,8 @@
 
 module ConnectionPoolBehavior
   def test_connection_pool
+    Thread.report_on_exception, original_report_on_exception = false, Thread.report_on_exception if Thread.respond_to?(:report_on_exception)
+
     emulating_latency do
       begin
         cache = ActiveSupport::Cache.lookup_store(store, pool_size: 2, pool_timeout: 1)
@@ -24,6 +26,8 @@ def test_connection_pool
         threads.each(&:kill)
       end
     end
+  ensure
+    Thread.report_on_exception = original_report_on_exception if Thread.respond_to?(:report_on_exception)
   end
 
   def test_no_connection_pool