REGTESTS: http_request_buffer: Increase client timeout to wait "slow" clients

The default client timeout is too small to be sure to always wait end of
slow clients (the last 2 clients use a delay to send their request). But it
cannot be increased because it will slow down the regtest execution. So a
dedicated frontend with a higher client timeout has been added. This
frontend is used by "slow" clients. The other one is used for normal
requests.
1 file changed