Fix GetNearest for scalar

* The return of the command is a tuple string, spearator ';'
* correctly convert timestamp and value

ArchiveExtractor.py

@@ -536,13 +536,13 @@ def _extract_scalar(attribute, method, date1, date2, db):
 
         # Unpack return
         try:
-            _date, _value = cmdreturn
+            _date, _value = cmdreturn.split(';')
         except TypeError:
             logger.error("Could not extract this chunk. Check the device extractor")
             return None
 
         # Fabricate return pandas.Series
-        d=pd.Series(index=[datetime.datetime.fromtimestamp(_date),], data=[_value,], name=attribute)
+        d=pd.Series(index=[datetime.datetime.fromtimestamp(int(_date)/1000),], data=[float(_value),], name=attribute)
 
         return d