AS-173: Delay in lock

Adding a 2 second delay after writing the state in `modify_state` so that it gets ample time (hopefully) to write the state to all cass nodes. This way the next read should get the latest state. This change should fix https://jira.rax.io/browse/AS-151. 

UPDATE: Based on discussion below we decided to solve the problem initially by using local timestamp. PR #621.