Fixes #6604: handle SIGHUP for cf-serverd

See https://dev.cfengine.com/issues/6604
Why doesn't this follow the same code path as below? Wouldn't it be better to do something like:

<pre>
-    if (config->agent_specific.daemon.last_validated_at &lt; validated_at)
+    if (config->agent_specific.daemon.last_validated_at &lt; validated_at
+        || IsRequestReloadConfig())
     {
+        if (IsRequestReloadConfig())
+        {
+            ClearRequestReloadConfig();
+            validated_at = time(NULL);
+        }
         /* Rereading policies now, so update timestamp. */
</pre>

or something along those lines.