snap: Start snap support.

- Create a snapcraft.yaml file in snap directory.
  Couldn't put this in packaging directory.
- Use make-snapcraft.py to generate the snapcraft file.
- Use make-snap to make the snap from the snapcraft file.
- Eris is confined to only access projects in home.
- os.setpriority doesn't work in snaps.
- eris-webserver is run as "eris.webserver".

packaging/make-snap

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+
+# Run this script from the project root.
+# i.e. ./packaging/make-snap
+
+
+set -e
+set -x
+
+
+# snap install lxd
+# lxd init  # Use defaults. Set size of loop device to at least 3GB.
+
+snapcraft clean --use-lxd
+snapcraft --use-lxd --debug
+sudo snap remove eris
+sudo snap install --dangerous eris_*_amd64.snap
+/snap/bin/eris -h