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/enter_environment

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+if test `id -u` -ne 0
+then
+    echo "$0 must be run as root."
+    return
+fi
+
+ROOT=test_environment
+
+if test -e "$ROOT"
+then
+    echo "Using existing environment in $ROOT."
+else
+    ./create_environment
+fi
+
+./mountpoints
+
+chroot "$ROOT" sudo -iu user "$@"