Don't differentiate root from non-root users

[ihucos]

This means:

• user namespace setup for root and nonroot users shal be the same
• this implies root users can have uidmaps configured
• the plashdata folder will be moved from /var/run/plash to /root/.plashdata

I thought a lot about this, I think it's the right think to do. moving the plashdata folder is a backward incompatible change.