Make sure the path exists on jail configure check

Merge:	releng/9.1.0
(cherry picked from commit ca4f0660fcb2e2eb2c5939ca79c5392bccb4d027)
Name dialog accordingly

Merge:	releng/9.1.0
(cherry picked from commit caa245d454d80450c867f712ff54fccc03fe969d)