Move owners.yaml parser from kernel-webhooks

Add main entry point to print labels of responsible subsystems for kernel source files.

Small fixes:

• import modules instead of symbols to ease mocking
• move yaml loading out of parser
• move test fixtures into separate files
• add pylint ignore
• add docstrings
• move private helpers into corresponding classes
• rename Entry to Subsystem
• simplify repeated glob test case

Part of pipeline-definition#207 (closed)

Signed-off-by: Michael Hofmann mhofmann@redhat.com