using local timestamp when inserting state
using ts in update too - incomplete
get_client_ts uses reactor.seconds()
started tests for local ts
code based on get_timestamp returning deferred
working timestamp changes

- get_timestamp() is expected to return value via Deferred to have easy
transition with zk counter
- using :ts in query
- ts is used while creating group and update launch/group config also
- added tests
Getting timestamp in common function - thanks @cyli

Using that as decorator that needs the timestamp
get_timestamp EPOCH as microseconds - thanks @cyli

since CASS stores timestamp with microseconds precision. This change
when deployed should have timestamp > existing one to not break any
existing group updates.
using timestamp when deleting group - thanks @cyli
with_timestamp tests - thanks @cyli

Also, not having `get_timestamp` method since get_client_ts is called
from with_timestamp method only. So with_timestamp calls get_client_ts
directly
Merge pull request #621 from rackerlabs/write_state_using_client_ts

AS-264: using local timestamp when changing group