scheduler consistency is QUORUM

It is possible that 1 api node deletes event and before it gets propogated to other cass nodes, other
api node picks the same event causing the same policy to get executed twice. So, read and writing at
quorum that guarantees consistency. The slower performance due to this is not really a concern since it
is happening in background.
using get_consistency_level instead of hard-coding
added tests for get_consistency_level
pep8 fix
using if instead - per @dreid
Merge pull request #318 from rackerlabs/scheduler_consistency

scheduler consistency is QUORUM