Support proot for jailing

[tokuhirom]

Ansible tower uses proot for jailing user scripts. http://docs.ansible.com/ansible-tower/2.2.0/html/installandreference/known_issues.html#playbooks-missing-access-to-necessary-data-due-to-proot-issues

If ansible semaphore supports proot or similar technology, users' script cannot break ansible semaphore server.

Ref. https://wiki.archlinux.org/index.php/Proot

[stefanux]

...and that should solve #1185 too.