This is the port of the early disk snapshot stuff we implemented for the Fedora 22 on the *f22-branch*. Turns out a better and reliable solution for a number of bugs these changes fixed and prevented won't be available any time soon so I'm porting this to the master branch to prevent serious regressions.
There have been some conflicts, basically all caused by the fixes for kickstart autopart missing passphrase and by changes done for the s390 stuff moved from blivet to libblockdev.