PEP8 (make qa) fixes for cobbler/template_api.py

cobbler/template_api.py:124:12: E713 test for membership should be 'not in'
cobbler/template_api.py:146:21: E128 continuation line under-indented for visual indent
cobbler/template_api.py:191:20: E713 test for membership should be 'not in'