Made the read quota take all GET_ALL keys into account
Releasing Voldemort 1.8.15
bdb native backup fixups

1. add message for native backup status
2. add bdb env config param: bdb.recovery.force.checkpoint
QuotaException causes delete failure

1) When QuotaException is thrown by delete, it fails the delete instead
of Quorum to decide the failure.
2) Added unit test to cover some part of the delete test case.