test: fix flaky test-http-dns-error

Under some conditions, the error received from getaddrinfo might
actually be EAGAIN, meaning the request should be retried. Allowing for
5 retries before erroring out.

Also replace one-off function with common.mustNotCall().

PR-URL: https://github.com/nodejs/node/pull/16534


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>