Code review comment for ~goneri/cloud-init:freebsd_set_password

> For non-FreeBSD, I don't understand why we would trade a single exec of chpasswd
> reading stdin list of users for an exec per-user.

cloud-init has two different way to set a password, this without any concrete benefit.
It's a lot of duplicated code and this creates case like this one where only one of the
two is broken. So, instead of adding an extra if/else block to deal with the current situation,
it sounds reasonable to me to just reduce this complexity.