Restrict single build per worker

Avoids too much of CPU burn and allows to more easily do codesign.

master.cfg

@@ -16,7 +16,7 @@ import master_private
 
 c['workers'] = []
 for slave in master_private.slaves:
-    c['workers'].append(Worker(slave['name'], slave['password']))
+    c['workers'].append(Worker(slave['name'], slave['password'], max_builds=1))
 
 # TCP port through which slaves connect
 c['protocols'] = {