Added new flag is_kpi to DataValue

Created by: stefanoborini

The flag will be set by the engine and used to recognise the data that must be sent back to the MCO.

force_bdss/core/data_value.py

-from traits.api import HasStrictTraits, Any, String, Enum
+from traits.api import HasStrictTraits, Any, String, Enum, Bool
 
 
 class DataValue(HasStrictTraits):
@@ -22,6 +22,9 @@ class DataValue(HasStrictTraits):
     #: A flag for the quality of the data.
     quality = Enum("AVERAGE", "POOR", "GOOD")
 
+    # Set by the engine. True if the data value contains a KPI.
+    is_kpi = Bool(False)
+
     def __str__(self):
 
         s = "{} {} = {}".format(
@@ -31,4 +34,8 @@ class DataValue(HasStrictTraits):
             s += " +/- {}".format(str(self.accuracy))
 
         s += " ({})".format(str(self.quality))
+
+        if self.is_kpi:
+            s += " (KPI)"
+
         return s