Add more tests for pw(8) useradd.

PR:		195832
Submitted by:	Robert O'Neil <oneil.rs@gmail.com>
Approved by:	will


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275653 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f