jail(3lua): add a jail.list() method

This is implemented as an iterator, reusing parts of the earlier logic
to populate jailparams from a passed in table.

The user may request any number of parameters to pull in while we're
searching, but we'll force jid and name to appear at a minimum.

(cherry picked from commit 6a7647eccd3ef35189c63a61b0ec8865fd559839)