don't automatically mount directories in chroot
fix problems with '/' and fix dependencies

1. '/' seems to be special. It is often treated as ''. This commit
   should fix most of the remaining places that were wrong.
2. We enforce this order:
   1. Create mountpoint
   2. mount it
   3. apply file resource (i.e. it is applied to the mounted file system)
   4. do anything that needs this directory (e.g. create a file in it)
fix regex for mounted directories

Old behaviour: '/a' matches '/var/caches/apt'. This means that '/a'
won't be mounted, if any directory which contains that string is
mounted.

New behaviour: Exact matching (no regex) on the whole path (unless
it contains special words).