REGTESTS: extend the default I/O timeouts and make them overridable

With the CI occasionally slowing down, we're starting to see again some
spurious failures despite the long 1-second timeouts. This reports false
positives that are disturbing and doesn't provide as much value as this
could. However at this delay it already becomes a pain for developers
to wait for the tests to complete.

This commit adds support for the new environment variable
HAPROXY_TEST_TIMEOUT that will allow anyone to modify the connect,
client and server timeouts. It was set to 5 seconds by default, which
should be plenty for quite some time in the CI. All relevant values
that were 200ms or above were replaced by this one. A few larger
values were left as they are special. One test for the set-timeout
action that used to rely on a fixed 1-sec value was extended to a
fixed 5-sec, as the timeout is normally not reached, but it needs
to be known to compare the old and new values.

reg-tests/http-messaging/srv_ws.vtc

@@ -11,9 +11,9 @@ feature ignore_unknown_macro
 haproxy hapsrv -conf {
 	defaults
 		mode http
-		timeout connect 5s
-		timeout client  5s
-		timeout server  5s
+		timeout connect "${HAPROXY_TEST_TIMEOUT-5s}"
+		timeout client  "${HAPROXY_TEST_TIMEOUT-5s}"
+		timeout server  "${HAPROXY_TEST_TIMEOUT-5s}"
 
 	frontend fe
 		bind "fd@${fe}"
@@ -40,9 +40,9 @@ haproxy hapsrv -conf {
 haproxy hap -conf {
 	defaults
 		mode http
-		timeout connect 1s
-		timeout client  1s
-		timeout server  1s
+		timeout connect "${HAPROXY_TEST_TIMEOUT-5s}"
+		timeout client  "${HAPROXY_TEST_TIMEOUT-5s}"
+		timeout server  "${HAPROXY_TEST_TIMEOUT-5s}"
 
 	# proto X ws h1 -> websocket on h1
 	listen li