rescue tag on VM now use the new max_concurrent arg in background decorator

cloudcontrol/node/hypervisor/domains/vm_tags.py

@@ -58,7 +58,7 @@ def uuid(dom):
     return dom.uuid.lower()
 
 
-@background
+@background(max_concurrent=3)
 def rescue(dom):
     """Is rescue mode enabled or not"""
     rescue_path = dom.hypervisor.handler.main.config.rescue_script