Fix pep8 F821

Fix these issues:
./manila/tests/windows/windowsutils.py:29:1: F821 undefined name 'cfg'
./manila/share/drivers/glusterfs.py:165:1: F821 undefined name 'config'

glusterfs.py: It should be config_file, adjust the message as well.

windowsutils.py: Add import for cfg.

Closes-Bug: #1351959

Change-Id: I9fa5087d2be6ecc262f9581d372f70f96373a387
Merge "Fix pep8 F821"