Add sleep before #term_and_wait_for_exit

We're expecting a callback from the ghostferry reacting to binlogs created by DataWriter, which can't be easily synchronized, since it's a goroutine inside the subprocess. Not ideal, but add a sleep to prevent cases where it doesn't happen before the TERM signal

test/integration/interrupt_resume_test.rb

@@ -131,6 +131,7 @@ def test_interrupt_resume_inline_verifier_with_datawriter
     ghostferry.on_status(Ghostferry::Status::AFTER_ROW_COPY) do
       batches_written += 1
       if batches_written >= 2
+        sleep 0.1
         ghostferry.term_and_wait_for_exit
       end
     end