Get rid of underscores in filenames, use dashes instead.
This is first part of cleanup in filenames.
"qubes_rpc" still untouched - will be in separate commit.
When /rw/home/user/.qubes-dispvm-customized is present use /rw/home/user
instead of default /etc/dispvm-dotfiles.tbz. Also make sure that /rw will not
remain mounted during DispVM creation.
