[9.0][FIX] database_cleanup: Isolate build (OCA#719)

* [FIX] database_cleanup: Isolate build
* Isolate `database_cleanup` into its own build in Travis file to fix OCA#689

* [FIX] database_cleanup: Remove KeyError assertion
* Remove KeyError assertion in tests due to PR in comment being merged

database_cleanup/tests/test_database_cleanup.py

@@ -59,15 +59,11 @@ def test_database_cleanup(self):
         self.registry._pure_function_fields.pop(
             'x_database.cleanup.test.model')
         purge_models = self.env['cleanup.purge.wizard.model'].create({})
-        with self.assertRaisesRegexp(KeyError,
-                                     'x_database.cleanup.test.model'):
-            # TODO: Remove with-assert of KeyError after fix:
-            # https://github.com/odoo/odoo/pull/13978/files#r88654967
-            purge_models.purge_all()
-            # must be removed by the wizard
-            self.assertFalse(self.env['ir.model'].search([
-                ('model', '=', 'x_database.cleanup.test.model'),
-            ]))
+        purge_models.purge_all()
+        # must be removed by the wizard
+        self.assertFalse(self.env['ir.model'].search([
+            ('model', '=', 'x_database.cleanup.test.model'),
+        ]))
 
         # create a nonexistent module
         self.module = self.env['ir.module.module'].create({