monitor: Fix "Scoreboard full" bug

If we don't specify MaxRequestWorkers, it seems like Apache 2.4
errors with:
AH03490: scoreboard is full, not at MaxRequestWorkers. Increase
ServerLimit.
Maybe because MaxRequestWorkers then defaults to a too high value
compared to ServerLimit and ThreadsPerChild.

/reviewed-on nexedi/slapos!263

stack/monitor/buildout.cfg

@@ -61,7 +61,7 @@ eggs =
 # Monitor templates files
 [monitor-httpd-conf]
 <= monitor-template-base
-md5sum = f2d6951670733de3b37c0ebe9eee343b
+md5sum = b5f42503799e7e770afce4097d3b75ae
 filename = monitor-httpd.conf.in
 
 [monitor-template-wrapper]

stack/monitor/templates/monitor-httpd.conf.in

@@ -2,6 +2,7 @@ PidFile "{{ parameter_dict.get('pid-file') }}"
 
 StartServers 1
 ServerLimit 1
+MaxRequestWorkers 4
 ThreadLimit 4
 ThreadsPerChild 4