User setup and erlang installation

A bit fiddly, but this lets us run a realistic erlang install script
from userspace, and then re-enter userspace later without wiping the
installation.

debian/install_scripts/get_erlang_zx

@@ -0,0 +1,3 @@
+#!/bin/sh
+sudo apt install erlang-base
+wget -q https://zxq9.com/projects/zomp/get_zx && bash get_zx

debian/install_scripts/user_setup

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Noninteractive, so that other scripts can install things with apt.
+export DEBIAN_FRONTEND=noninteractive
+
+# Overwrite locale setting specified before the chroot
+export LANG=C
+export LC_ALL=C
+
+# Install sudo, since most user-facing scripts will use sudo
+apt install sudo
+
+# Add a passwordless sudoer
+useradd -m -s /bin/bash -G sudo user
+passwd -d user
+echo "user ALL=(ALL) NOPASSWD:ALL" > "/etc/sudoers.d/user"
+chmod 0440 "/etc/sudoers.d/user"
+
+# Copy the install scripts into their home directory
+cp -r ~/install_scripts /home/user
+chown -R user:user /home/user/install_scripts
+
+# su to this new user... Or sudo -iu, since we want to pass in arguments too.
+cd /home/user
+sudo -iu user "$@"