The problem here is that payload is setting up storage when
PayloadManager run a thread but the user could do steps which
will call the spaceRequired() method sooner.
Now the behavior is the same as it was with the old spaceRequired
method for the variant when storage is not set.
Resolves: rhbz#1271657
*This is more general (hot)fix for the bugs "NoneType has no mountpoint"*
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To view this pull request on github, visit
https://github.com/rhinstaller/anaconda/pull/530