Existence of both BucketNotFoundException and BucketDoesNotExistException not consistent with RFC

In the SDK we are raising BucketDoesNotExistException instead of BucketNotFoundException from the bucket management APIs when an operation requires a bucket to be present. 

There are some failures in FIT where BucketNotFound is expected instead of BucketDoesNotExistException:

• BucketManagerTest.dropNonExistentBucket
• BucketManagerTest.getNonExistentBucket

Might or might not need an SDK change. If not, we might just need to update the performer and/or driver to handle BucketDoesNotExistException.