Fixed review comments by Adam.

- use adduser instead of useradd.

live-build/ubuntu-cpc/hooks/042-vagrant.binary

@@ -72,7 +72,7 @@ chroot ${mount_d} apt-get clean
 # Vagrant users expect a "vagrant" user with a "vagrant" username.
 # See https://www.vagrantup.com/docs/boxes/base.html
 # Note: We decided NOT to allow root login with a default password.
-chroot ${mount_d} useradd -m vagrant -s /bin/bash
+chroot ${mount_d} adduser vagrant
 echo "vagrant:vagrant" | chroot ${mount_d} chpasswd
 
 # The vagrant user should have passwordless sudo.
@@ -87,7 +87,7 @@ chroot ${mount_d} mkdir -p /home/vagrant/.ssh
 cat << EOF > ${mount_d}/home/vagrant/.ssh/authorized_keys
 ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA6NF8iallvQVp22WDkTkyrtvp9eWW6A8YVr+kz4TjGYe7gHzIw+niNltGEFHzD8+v1I2YJ6oXevct1YeS0o9HZyN1Q9qgCgzUFtdOKLv6IedplqoPkcmF0aYet2PkEDo3MlTBckFXPITAMzF8dJSIFo9D8HfdOV0IAdx4O7PtixWKn5y2hMNG0zQPyUecp4pzC6kivAIhyfHilFR61RGL+GPXQ2MWZWFYbAGjyiYJnAmCP3NOTd0jMZEnDkbUvxhMmBYSdETk1rRgm+R4LOzFUGaHqHDLKLX+FIPKcF96hrucXzcWyLbIbEgE98OHlnVYCzRdK8jlqm8tehUc9c9WhQ== vagrant insecure public key
 EOF
-chroot ${mount_d} chown -R vagrant: /home/vagrant/.ssh
+chroot ${mount_d} chown -R vagrant:vagrant /home/vagrant/.ssh
 
 umount_disk_image "$mount_d"
 rmdir "$mount_d"