Allow persister to handle retention policies in influx

Change-Id: I99f3bc265f347c805fc13cad5e857f70f791851a

monasca_persister/repositories/persister.py

@@ -55,10 +55,13 @@ class Persister(object):
 
             self._data_points = []
             self._consumer.commit()
-        except Exception:
-            LOG.exception("Error writing to database: {}"
-                          .format(self._data_points))
-            raise
+        except Exception as ex:
+            if ex.message.startswith("400: partial write: points beyond retention policy dropped"):
+                LOG.info("Some points older than retention policy were dropped")
+            else:
+                LOG.exception("Error writing to database: {}"
+                              .format(self._data_points))
+                raise ex
 
     def run(self):
         try: