Dont assume that sigint wasnt masked when invoking ruby tests

src/ruby/end2end/killed_client_thread_client.rb

@@ -35,7 +35,7 @@ def main
                                       :this_channel_is_insecure)
     stub.echo(Echo::EchoRequest.new(request: 'hello'))
     fail 'the clients rpc in this test shouldnt complete. ' \
-      'expecting SIGINT to happen in the middle of the call'
+      'expecting SIGTERM to happen in the middle of the call'
   end
   thd.join
 end

src/ruby/end2end/killed_client_thread_driver.rb

@@ -69,9 +69,9 @@ def main
     call_started_cv.wait(call_started_mu) until call_started.val
   end
 
-  # SIGINT the child process now that it's
+  # SIGTERM the child process now that it's
   # in the middle of an RPC (happening on a non-main thread)
-  Process.kill('SIGINT', client_pid)
+  Process.kill('SIGTERM', client_pid)
   STDERR.puts 'sent shutdown'
 
   begin
@@ -88,8 +88,8 @@ def main
   end
 
   client_exit_code = $CHILD_STATUS
-  if client_exit_code.termsig != 2 # SIGINT
-    fail 'expected client exit from SIGINT ' \
+  if client_exit_code.termsig != 15 # SIGTERM
+    fail 'expected client exit from SIGTERM ' \
       "but got child status: #{client_exit_code}"
   end