Fix issue where we didn't delete robots immediately under a namespace

This could result in "hanging" robot accounts, although that would only leak the names of said accounts. Now we delete them immediately AND we proactively delete them before replacing the namespace (just to be sure)

data/migrations/versions/5b7503aada1b_cleanup_old_robots.py

@@ -0,0 +1,23 @@
+"""Cleanup old robots
+
+Revision ID: 5b7503aada1b
+Revises: 224ce4c72c2f
+Create Date: 2018-05-09 17:18:52.230504
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '5b7503aada1b'
+down_revision = '224ce4c72c2f'
+
+from alembic import op
+import sqlalchemy as sa
+
+from util.migrate.cleanup_old_robots import cleanup_old_robots
+
+def upgrade(tables):
+  cleanup_old_robots()
+
+def downgrade(tables):
+  # Nothing to do.
+  pass