REGTESTS: http-messaging: make the /c5 abort land during the retries

REGTESTS: http-messaging: make the /c5 abort land during the retries

The previous attempt at making this case robust, which raised the
connect timeout so that the client abort is noticed before the retries
are over, was not enough: the client closes immediately after its
request, so under load the close is sometimes seen while the request is
still being parsed, and the transaction is then logged as "CH--" with a
400 instead of the expected "CC--".

The client now waits fifty milliseconds before closing, which leaves
haproxy the time to read the request and to start connecting, and the
raised connect timeout gives the abort a full second to be noticed.
Twenty runs in parallel with the machine loaded pass.