consolidate logger logic to shared

[ryandeivert]

to: @chunyong-lin
cc: @airbnb/streamalert-maintainers
size: medium

Background

I'm going to be adding another Lambda function soon, and it pains me to copy/pasta the old logger creation again.

Changes

I've removed how loggers were previously created and centralized in the shared module.

• Adding central/shared logger.py along with tests
• Updating all modules to use shared logger logic
• Updating apps lambda packaging logic to include shared module

Testing

Updating all unit tests

[chunyong-lin]

Beautiful!
LGTM, one question from my curiosity.

[coveralls]

Coverage increased (+0.4%) to 97.31% when pulling 01e37c7 on ryandeivert-consolidate-logger into 777f423 on master.