add shortIdentifier attribute to Agent

Author: blacktwin

plexapi/media.py

@@ -674,4 +674,5 @@ def _loadData(self, data):
         self.hasAttribution = data.attrib.get('hasAttribution')
         self.hasPrefs = data.attrib.get('hasPrefs')
         self.identifier = data.attrib.get('identifier')
-        self.primary = data.attrib.get('primary')
+        self.primary = data.attrib.get('primary')
+        self.shortIdentifier = self.identifier.rsplit('.', 1)[1]