return as unchanged if macro update is unnecessary

lib/ansible/modules/extras/monitoring/zabbix_hostmacro.py

@@ -147,6 +147,8 @@ class HostMacro(object):
     # update host macro
     def update_host_macro(self, host_macro_obj, macro_name, macro_value):
         host_macro_id = host_macro_obj['hostmacroid']
+        if host_macro_obj['macro'] == '{$'+macro_name+'}' and host_macro_obj['value'] == macro_value:
+            self._module.exit_json(changed=False, result="Host macro %s already up to date" % macro_name)
         try:
             if self._module.check_mode:
                 self._module.exit_json(changed=True)