No need to print migration message on fresh ckan install (eg travis)

ckan/migration/versions/089_package_activity_migration_check.py

@@ -16,17 +16,23 @@ def upgrade(migrate_engine):
     should run the package activity migration, so that the Activity Stream can
     display the detailed history of datasets:
 
-       python migrate_package_activity.py -c /etc/ckan/production.ini
+        python migrate_package_activity.py -c /etc/ckan/production.ini
 
     Once you've done that, the detailed history is visible in Activity Stream
     to *admins only*. However you are encouraged to make it available to the
     public, by setting this in production.ini:
 
-       ckan.auth.public_activity_stream_detail = true
+        ckan.auth.public_activity_stream_detail = true
 
     More information about all of this is here:
     https://github.com/ckan/ckan/wiki/Migrate-package-activity
                 '''.format(num_unmigrated=num_unmigrated_dataset_activities))
     else:
-        print(u'You have no unmigrated package activities - you do not need to'
-              'run migrate_package_activity.py.')
+        # there are no unmigrated package activities
+        are_any_datasets = bool(
+            migrate_engine.execute(u'SELECT id FROM PACKAGE LIMIT 1').rowcount)
+        # no need to tell the user if there are no datasets - this could just
+        # be a fresh CKAN install
+        if are_any_datasets:
+            print(u'You have no unmigrated package activities - you do not '
+                  'need to run migrate_package_activity.py.')