testcase: improve leaked partitions detection and cleanup

- We should only try to remove leaked partitions if we detected some,
  otherwise it may produce a strange message "unable to delete leaked
  partitions".
- If some supervisor configuration is still present after partition
  deletion, they must be removed not to block next test and the current
  test must be marked failed.

slapos/testing/testcase.py

@@ -461,6 +461,11 @@ class SlapOSInstanceTestCase(unittest.TestCase):
       cls.slap.stop()
     except:
       cls.logger.exception("Error during stop")
+    leaked_supervisor_configs = glob.glob(
+        os.path.join(cls.slap.instance_directory, 'etc', 'supervisord.conf.d', '*.conf'))
+    if leaked_supervisor_configs:
+      [os.unlink(config) for config in leaked_supervisor_configs]
+      raise AssertionError("Test leaked supervisor configurations: %s" % leaked_supervisor_configs)
 
   @classmethod
   def requestDefaultInstance(cls, state='started'):