Cleanup the blacklist plugin
Cleanup the blacklist plugin

Just cleanup a lot of small annoyances:
- parse level at config load, not runtime
- don't use list+index which have to be explained in the comment
- use any() instead of manual loop
- use dict.get(...) with default instead of an `if` ladder

No changes in functionality.

Change-Id: Ia65537fca2828685cd18c8a706cf47bf56ab8918

pombredanne/bandit,chair6/bandit,stackforge/bandit,pombredanne/bandit,stackforge/bandit