Avoid removing the track if set to latest in channel normalization

Fixes #863

Author: cderici

juju/origin.py

@@ -97,7 +97,9 @@ def parse(s):
         return Channel(track, risk)
 
     def normalize(self):
-        track = self.track if self.track != "latest" else ""
+        # TODO (cderici): this is essentially a noop, needs to be revised in both
+        #  2.9 and 3.x
+        track = self.track if self.track != "" else ""
         risk = self.risk if self.risk != "" else ""
         return Channel(track, risk)