Import only .py files when importing rules

[austinbyers]

to: @ryandeivert
cc: @airbnb/streamalert-maintainers
size: small

Background

Users should be able to have non-Python files in the rules/ directory (e.g. README, REVIEWERS, etc). The current rules import logic imports all files except *.pyc, .* and __init__.*. This means files like rules/README are also imported, which causes an ImportError.

Changes

• Change rule import logic to import all *.py files in rules/ and matchers/ except __*
• Refactor rule import logic into 3 unit-testable functions.
• Rename test_main.py to test_init.py (since it tests LOGGER during __init__.py)
• Added new unit tests for rule import logic.

Testing

• Added new unit tests for rule import logic.
• Verified that the rule integration tests covered the same set of rules as before (all rules are still imported)

[coveralls]

Coverage increased (+0.5%) to 95.397% when pulling b71ada5 on austin-allow-non-rules-files into 5cebabd on master.

[coveralls]

Coverage increased (+0.5%) to 95.397% when pulling b71ada5 on austin-allow-non-rules-files into 5cebabd on master.

[ryandeivert]

This is great!! Thanks for doing it :)

[coveralls]

Coverage increased (+0.5%) to 95.397% when pulling f4f71db on austin-allow-non-rules-files into 5cebabd on master.