[2136] moved invoking update_modules() to outside of the method

When the set command was used for collecting statistics data, the action was
randomly. But in the case that periodical polling is used for collecting
statistics data, update_modules doesn't need to be invoked so many times every
time update_statistics_data is invoked. Invoking update_module() causes an IO
wait for receiving statistics spec from Cfgmgr.

src/bin/stats/stats.py.in

@@ -195,6 +195,7 @@ class Stats:
         # set a absolute timestamp polling at next time
         self.next_polltime = get_timestamp() + self.get_interval()
         # initialized Statistics data
+        self.update_modules()
         if self.update_statistics_data(
             self.module_name,
             self.cc_session.lname,
@@ -288,6 +289,7 @@ class Stats:
                 pass
 
         # update statistics data
+        self.update_modules()
         while len(_statistics_data) > 0:
             (_module_name, _lname, _args) = _statistics_data.pop(0)
             if self.update_statistics_data(_module_name, _lname, _args):
@@ -412,7 +414,7 @@ class Stats:
         module. If it can't find specified statistics data, it raises
         StatsError.
         """
-        self.update_statistics_data()
+        self.update_modules()
         if owner and name:
             try:
                 return {owner:{name:self.statistics_data[owner][name]}}
@@ -472,7 +474,6 @@ class Stats:
             return ret
 
         # Firstly, it gets default statistics data in each spec file.
-        self.update_modules()
         statistics_data = {}
         for (name, module) in self.modules.items():
             value = get_spec_defaults(module.get_statistics_spec())