user creation omnibus

[classabbyamp]

• installer: use chroot instead of -R arg for useradd/chpasswd
  • fixes #18
  • fixes #181
  • fixes #306
• installer: hide USERPASSWORD in settings
  • fixes #240
• installer: default hostname to 'void' if unset
  • just something i noticed along the way

[classabbyamp]

I've reported the useradd issue to upstream: https://github.com/shadow-maint/shadow/issues/692