Description of problem:

anaconda 18.8 exception report
Traceback (most recent call first):
  File "/usr/lib64/python2.7/site-packages/pyanaconda/errors.py", line 248, in cb
    StorageError.PartitioningWarning: self._partitionWarningHandler,
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/partitioning.py", line 309, in doAutoPartition
    if errorHandler.cb(exn) == ERROR_RAISE:
  File "/usr/lib64/python2.7/site-packages/pyanaconda/kickstart.py", line 269, in execute
    doAutoPartition(storage, ksdata)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/kickstart.py", line 1605, in doKickstartStorage
    ksdata.autopart.execute(storage, ksdata, instClass)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 333, in _doExecute
    doKickstartStorage(self.storage, self.data, self.instclass)
  File "/usr/lib64/python2.7/threading.py", line 504, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/threads.py", line 87, in run
    threading.Thread.run(self, *args, **kwargs)
AttributeError: 'module' object has no attribute 'PartitioningWarning'

Version-Release number of selected component (if applicable):
anaconda 18.8

How reproducible:
always

Steps to Reproduce:
1. Start vnc installation on s390x
2. go to "Installation destination"
3. select all (3) dasd drives
4. select Done
5. go again to "Installation destination"
6. unselect one (the last one on the screen) dasd drive
7. select Done
  
Actual results:
traceback

Expected results:
no traceback

Additional info:
Tested only on s390x, I haven't tried other arches.