ad: path detection in getvolbypath(), bug #570

The fix for bug #563 broke ad file utilities, bug #570.

Authored-by: gaaronk
Reviewed-by: Ralph Boehme <rb@sernet.de>
Use realpath_safe() for getting the absolute path

Authored-by: gaaronk
Reviewed-by: Ralph Boehme <rb@sernet.de>