Started scheduler schema change

Events stored based on minute they will execute.
future time check in minute
Add tests for ensuring force delete args are handled correctly
Update the config, rather than set a completely new one
Call obey_config_change to ensure servers get deleted.
started bucket based impl
in middle impl
scheduler methods outside the class - pure :)
Merge branch 'master' into buckets

Conflicts:
	otter/models/cass.py
	otter/scheduler.py

Taking scheduler newer code
Scheduler test case methods added

Just need to implement them :)
reverted json_schema changes
rbac tests
skipped tests
Merge branch 'master' into auto-730-test-rbac-roles
Scheduler tests working
was not giving set to partition - fixed

- giving list of buckets to store and it'll cycle over it
- Some comments in scheduler.py
lint fixes
model change related to scheduler

policy table has version column that gets updated whenever its
respective event is added to event table. scheduler ensures that version
matches before executing event. This way, we dont bother deleting event
whenever a policy is deleted or updated. When a policy is updated, a new
event with new version is added. The old event when picked up will not
get executed since its respective policy (with that version) is not
there. Added version=None to get_policy that checks the version before
returning.

Refactored test_cass_models into seperate class for testing add_policy
and update_policy
Not deleting events on group delete
mock models fixed