Add system's requirements.txt, enforce flake8 linter

Fix style issues in functional tests.

system/t06_publish/__init__.py

@@ -1,14 +1,3 @@
 """
 Testing publishing snapshots
 """
-
-from .fs_endpoint import *
-from .drop import *
-from .show import *
-from .list import *
-from .repo import *
-from .snapshot import *
-from .switch import *
-from .update import *
-from .s3 import *
-from .swift import *