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/lua/bad_http_clt_req_duration.vtc

@@ -38,9 +38,9 @@ haproxy h1 -conf {
         lua-load ${testdir}/bad_http_clt_req_duration.lua
 
     defaults
-        timeout client 1s
-        timeout server 1s
-        timeout connect 1s
+        timeout client "${HAPROXY_TEST_TIMEOUT-5s}"
+        timeout server "${HAPROXY_TEST_TIMEOUT-5s}"
+        timeout connect "${HAPROXY_TEST_TIMEOUT-5s}"
 
     frontend f1
         mode http

reg-tests/lua/close_wait_lf.vtc

@@ -26,8 +26,8 @@ syslog Slog -level info -repeat 100 {
 
 haproxy h1 -conf {
     defaults
-        timeout client  1s
-        timeout connect 1s
+        timeout client  "${HAPROXY_TEST_TIMEOUT-5s}"
+        timeout connect "${HAPROXY_TEST_TIMEOUT-5s}"
 
     global
         lua-load ${testdir}/close_wait_lf.lua