add os tql tag

TQL

@@ -99,6 +99,7 @@ arch: hardware architecture (x86/x64)
 uname: output of uname command
 uptime: uptime of hostname
 load: load average
+os: operating system (linux/windows)
 alloc: host is allowed to be selected to a migration
 hvm: hardware virtualisation enabled
 nvm: vm count on an hypervisor

cccli/handler.py

@@ -43,7 +43,7 @@ class CliHandler(RpcHandler):
     def get_tag_os(self, resolve):
         '''Return Operating system tag'''
         if resolve:
-            return { "value": platform.system(), "ttl": -1 }
+            return { "value": platform.system().lower(), "ttl": -1 }
         return { "ttl": -1 }
 
     def get_tag_uname(self, resolve):