Was able to get 2s wait times with 500 concurrent requests on a fast machine;
a slower machine could possibly see similar delays with a single connection.
Fixes#6220
This helps the test to pass safely in semaphore CI.
Based on my manual testing, it may take at most 500ms to return
error in semaphore CI, so I set 1s as a safe value.
As we move to container-based infrastructure testing env
on travis, the tcp write buffer is more than 1MB. Change
the test according to the change on the testing env.
