Description of problem:
I have thin pool with thin volumes (existing linux installation)

Version-Release number of selected component (if applicable):
20.25-1

How reproducible:
100%

Steps to Reproduce:
1. start anaconda on disk which already contains thin-pool with thin volumes

Actual results:
Anaconda does not start.
Nothing logged on console.

Proposing as beta blocker though I am not sure which requirement is the best match, I guess following alpha may apply:

> Installer must run
> 
> - The installer must run when launched normally from the release-blocking images.


Expected results:
Anaconda should start (and report issues, if there are any.)
If there is any unhandled expection in anaconda, it should be reported on text console.

Additional info:
Starting anaconda in text mode raises TypeError: __init__() got an unexpected keyword argument 'segType' exception:

===============================================================================
An unknown error has occurred
===============================================================================
anaconda 20.25-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 1304, in handleVgLvs
    exists=True)
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 1404, in handleUdevLVMPVFormat
    self.handleVgLvs(vg_device)
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 1691, in handleUdevDeviceFormat
    self.handleUdevLVMPVFormat(info, device)
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 1075, in addUdevDevice
    self.handleUdevDeviceFormat(info, device)
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 1916, in _populate
    self.addUdevDevice(dev)
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 1860, in populate
    self._populate()
  File "/usr/lib/python2.7/site-packages/blivet/__init__.py", line 417, in reset
    self.devicetree.populate(cleanupOnly=cleanupOnly)
  File "/usr/lib/python2.7/site-packages/blivet/__init__.py", line 144, in storageInitialize
    storage.reset()
  File "/usr/lib64/python2.7/threading.py", line 764, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/threads.py", line 168, in run
    threading.Thread.run(self, *args, **kwargs)
TypeError: __init__() got an unexpected keyword argument 'segType'