Support 'createhome' parameter in salt.modules.pw_user.add on FreeBSD

This adds support for the createhome parameter for `salt.modules.pw_user.add` in FreeBSD similar to the changes from pull request #5342 for `salt.modules.useradd.add`

By default it is `True`, as in useradd.py, and unless it's `False`, the `-m` argument is added to `pw`.