kas: Better support introspection

PEP8:
"""
To better support introspection, modules should explicitly declare the
    names in their public API using the __all__ attribute.
"""

flake8 reports

./kas/kas.py:51:1: F401 '.build' imported but unused
./kas/kas.py:52:1: F401 '.shell' imported but unused

Signed-off-by: Daniel Wagner <daniel.wagner@siemens.com>

kas/kas.py

@@ -51,6 +51,8 @@ from .libkas import kasplugin
 from . import build
 from . import shell
 
+__all__ = ['build', 'shell']
+
 __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017-2018'