scheduler locking bugfix

Creating BasicLock object on every scheduler run instead of reusing same
object throughout.

Having same BasicLock object had one claimId being used in every lock
acquistion that caused problem when 2 nodes tried to get lock at same
time. Because of the way Cass deletes rows, inserting row with same
claimId that was deleted earlier just enables the earlier row. And
selecting ordered rows returns older row first causing the confusion
Merge pull request #388 from rackerlabs/scheduler_locking_bugfix

scheduler locking bugfix