Implement "_check_no_open_files_on_filesystem()" as common function and use it in ftjail. It checks for open files and memory mapping on a given file system. It uses the standard command "fstat -m -f <PATH>".

syntax: regexp

^work-default/
^work-alldeps/
^docs/_build/
^docs/_venv.*/
^_venv.*/
^tests/fbhyve/bootvars.fd