REGTESTS: http-messaging: Fix http_fail_cnt_body to succeed with small timeouts

REGTESTS: http-messaging: Fix http_fail_cnt_body to succeed with small timeouts

http_fail_cnt_body.vtc script was failing when small timeouts were used. The
script tries to detect client or server aborts during payload forwarding on
the other side. Because "http-no-delay" option was not set, a 200ms delay
could be observed to forward the server response. So with small timeouts,
the server timeout was hit before the client abort. It is now fixed.

In addition the delay before emitting CLI commands was removed.

This patch should be backported as far as 2.8.