Swift doesn't process corrupted hashes properly

Issue

• The following errors occur periodically on object storage node after some hashes.pkl file gets corrupted:

  May  9 08:45:12 overcloud-controller-1 object-server:
  ERROR __call__ error with REPLICATE /d1/636 :
  Traceback (most recent call last):
      File "/usr/lib/python2.7/site-packages/swift/obj/server.py", line 
  1150, in __call__
          res = getattr(self, req.method)(req)
      File "/usr/lib/python2.7/site-packages/swift/common/utils.py", line 1672, in _timing_stats
          resp = func(ctrl, *args, **kwargs)
      File "/usr/lib/python2.7/site-packages/swift/obj/server.py", line 1123, in REPLICATE
          device, partition, suffixes, policy)
      File "/usr/lib/python2.7/site-packages/swift/obj/diskfile.py", line 1408, in get_hashes
          self._get_hashes, device, partition, policy, recalculate=suffixes)
      File "/usr/lib/python2.7/site-packages/swift/common/utils.py", line 3657, in tpool_reraise
          raise resp
  TypeError: must be encoded string without NULL bytes, not str
  
  May  9 08:45:13 overcloud-controller-1 object-server: Error syncing partition:
  Traceback (most recent call last):
      File "/usr/lib/python2.7/site-packages/swift/obj/replicator.py", line 407, in update
          self.replication_cycle))
      File "/usr/lib/python2.7/site-packages/swift/common/utils.py", line 36 57, in tpool_reraise
          raise resp
  TypeError: must be encoded string without NULL bytes, not unicode