REGTESTS: abortonclose: Fix some race conditions

Depending on the timing, the second client that should be reported as a
client abort during connection attempt ("CC--" termination state) is
sometime logged as a server close ("SC--" termination state) instead. It
happens because sometime the connection failure to the server s1 is detected
by haproxy before the client c2 aborts. There is no retries and the
connection timeout is set to 100ms. So, to work, the client abort must be
performed and detected by haproxy in less than 100ms.

To fix the issue, the c2 client is now routed to a backend with a connection
timeout set to 1 second and 10 retries. It should be large enough to detect
the client aborts (~10s)

In addition, there is another race condition when the script is
started. sometime, server s1 is not stopped when the first client sends its
request. So a barrier was added to be sure it is stopped before starting to
send requests. And we wait to be sure the server is detected as DOWN to
unblock the barrier. It is performed by a dedicated backend with an
healthcheck on the server s1.

This patch should solve issue #1664.

reg-tests/http-messaging/http_abortonclose.vtc

@@ -7,10 +7,12 @@ feature ignore_unknown_macro
 feature cmd "$HAPROXY_PROGRAM -cc 'version_atleast(2.5-dev0)'"
 #REGTEST_TYPE=slow
 
+# b0 : Wait s1 was detected as DOWN to be sure it is stopped
 # b1 : Don't send /c4 before /c3 was received by s2 server
 # b2 : Don't finish c2 before c1 and c3 before c4 (from syslog POV)
 # b3 : finish c3 before s2
 
+barrier b0 cond 2 -cyclic
 barrier b1 cond 2 -cyclic
 barrier b2 cond 2 -cyclic
 barrier b3 cond 2 -cyclic
@@ -32,11 +34,15 @@ server s2 {
 } -start
 
 syslog S -level info {
+    recv alert
+    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: Server check/srv1 is DOWN.*"
+    barrier b0 sync
+
     recv
-    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: .* .* fe1 be1/srv1 [0-9]*/[0-9]*/-1/-1/[0-9]* 503 .* - - SC-- .* .* \"GET /c1 HTTP/1\\.1\""
+    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: .* .* fe1 be1_1/srv1 [0-9]*/[0-9]*/-1/-1/[0-9]* 503 .* - - SC-- .* .* \"GET /c1 HTTP/1\\.1\""
     barrier b2 sync
     recv
-    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: .* .* fe1 be1/srv1 [0-9]*/[0-9]*/-1/-1/[0-9]* -1 .* - - CC-- .* .* \"GET /c2 HTTP/1\\.1\""
+    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: .* .* fe1 be1_2/srv1 [0-9]*/[0-9]*/-1/-1/[0-9]* -1 .* - - CC-- .* .* \"GET /c2 HTTP/1\\.1\""
 
     recv
     expect ~ "[^:\\[ ]*\\[[0-9]*\\]: .* .* fe2 be2/<NOSRV> [0-9]*/[0-9]*/-1/-1/[0-9]* -1 .* - - CQ-- .* .* \"GET /c4 HTTP/1\\.1\""
@@ -65,7 +71,8 @@ haproxy h1 -conf {
         option httplog
         log ${S_addr}:${S_port} local0 debug err
         bind "fd@${fe1}"
-        use_backend be1
+        use_backend be1_1 if { path /c1 }
+        use_backend be1_2 if { path /c2 }
 
     frontend fe2
         option httplog
@@ -73,13 +80,25 @@ haproxy h1 -conf {
         bind "fd@${fe2}"
         use_backend be2
 
-    backend be1
+    backend be1_1
+        server srv1 ${s1_addr}:${s1_port}
+
+    backend be1_2
+        timeout connect 1s
+        retries 10
         server srv1 ${s1_addr}:${s1_port}
 
     backend be2
         server srv1 ${s2_addr}:${s2_port} maxconn 1
+
+    backend check
+        server srv1 ${s1_addr}:${s1_port} check
+        log ${S_addr}:${S_port} local0 debug alert
 } -start
 
+# Wait s1 was detected as DOWN
+barrier b0 sync
+
 # No server, wait all connection retries : SC--
 client  c1 -connect ${h1_fe1_sock} {
     txreq -url /c1