Build and load binder/ashmem kernel modules on service start

As both kernel modules are not part of the standard Ubuntu kernel we
need to build and load them at runtime. We bundle this together with
the container manager start and reuse the classic snap scripts to do
the actual build in a proper environment.

scripts/classic

@@ -0,0 +1,63 @@
+#!/bin/sh
+
+set -e
+
+ROOT=$SNAP_COMMON/classic
+
+# $1: source
+# $2: target
+# $3: if not empty, bind mount will be read-only
+# note that we do NOT clean these up at the end, as the user might start many
+# classic shells in parallel; we could start all of them in their own mount
+# namespace, but that would make the classic shell less useful for
+# developing/debugging the snappy host
+do_bindmount() {
+    if ! mountpoint -q "$ROOT/$2"; then
+        if [ -d "$1" -a ! -L "$1" ]; then
+            mkdir -p "$ROOT/$2"
+        fi
+        mount --make-rprivate --rbind -o rbind "$1" "$ROOT/$2"
+        if [ -n "${3:-}" ]; then
+            mount --rbind -o remount,ro "$1" "$ROOT/$2"
+        fi
+    fi
+}
+
+if [ "$(id -u)" != "0" ]; then
+    echo "needs to run as root"
+    exit 1
+fi
+
+if [ ! -d $ROOT ]; then
+    # IMPORTANT: do not run the classic.create as this will run it with
+    #            snap-confine again and this will cause havoc with current
+    #            snap-confine
+    $SNAP/bin/create
+fi
+
+# FIXME: confinement will prevent this
+do_bindmount /home /home
+do_bindmount /run /run
+do_bindmount /proc /proc
+do_bindmount /sys /sys
+do_bindmount /dev /dev
+do_bindmount / /snappy
+
+SUDO_USER=root
+
+# fix LP: #1619455
+cp -a /var/lib/extrausers/* $ROOT/var/lib/extrausers/
+cp -a /etc/sudoers.d/* $ROOT/etc/sudoers.d/
+
+# assemble command line
+DEVPTS="mount -o mode=666,ptmxmode=666 -t devpts devpts /dev/pts"
+SUDOCMD="sudo debian_chroot=classic -u ${SUDO_USER} -i $@"
+# FIXME: workaround for https://bugs.launchpad.net/snappy/+bug/1611493
+SCRIPT="script --quiet --return --command \"$SUDOCMD\" /dev/null"
+
+CMD="$DEVPTS; $SCRIPT"
+
+systemd-run --quiet --scope --unit=classic-$$.scope --description="Classic shell" chroot "$ROOT" sh -c "$CMD"
+
+# kill leftover processes after exiting, if it's still around
+systemctl stop classic-$$.scope 2>/dev/null || true