nfs: add export option 'all_root' to map all users to local root

Target: master
Ached-by: Albert Rossi
pseudofs: inherit parent dirs uid/gid in all_root option is used

Hosts to which all_root export option is applied
can create files and directories in any directory. Additionally,
all new objects inherit uid and gid from the parent directory.
 This is a special behavior make dcache with ownCloud a unique
solution, which will allow to share user data directories with
regular access methods in parallel to ownCloud, which runs under
uid of httpd process (apache).

Target: master
Ached-by: Albert Rossi