Fix migration wrt invalid constraints.

charmworld/migrations/versions/026_convert_comma_constraints.py

Index: charmworld/migrations/versions/026_convert_comma_constraints.py
=== modified file 'charmworld/migrations/versions/026_convert_comma_constraints.py'
--- charmworld/migrations/versions/026_convert_comma_constraints.py	2014-04-22 14:05:42 +0000
+++ charmworld/migrations/versions/026_convert_comma_constraints.py	2014-04-22 18:22:29 +0000
@@ -28,7 +28,16 @@
     for bundle_data in bundles:
         if 'inherits' in bundle_data['data']:
             del bundle_data['data']['inherits']
-        convert_bundle_constraints(bundle_data['data'])
+        try:
+            convert_bundle_constraints(bundle_data['data'])
+        except ValueError as e:
+            # This bundle has constraints that are invalid or no longer
+            # supported.  Simply skip the bundle.
+            log.warning('Bundle has invalid constraint.  Skipping {}'.format(
+                bundle_data['_id']))
+            log.warning(e.message)
+            target_db.bundles.remove(bundle_data['_id'])
+            continue
         basket_id = '{}/{}'.format(
             bundle_data['basket_name'],
             bundle_data['basket_revision'])