REGTESTS: Add script to test abortonclose option

REGTESTS: Add script to test abortonclose option

This script test abortonclose option for HTTP/1 client only. It may be
backported as far as 2.0. But on the 2.2 and prior, the syslog part must be
adapted to catch log messages emitted by proxy during HAProxy
startup. Following lines must be added :

    recv
    expect ~ "[^:\\[ ]\\[${h1_pid}\\]: Proxy fe1 started."
    recv
    expect ~ "[^:\\[ ]\\[${h1_pid}\\]: Proxy fe2 started."

(cherry picked from commit 16b37510bc1114ab7603240f8bbfeea20e5ee23b)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>