roles/homeassistant: Deploy Home Assistant

This commit introduces a *homeassistant* role that installs and sets up
Home Assistant using `pip`.

roles/homeassistant/files/hass.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec /var/lib/homeassistant/.local/bin/hass

roles/homeassistant/files/homeassistant.service

@@ -0,0 +1,12 @@
+# vim: set ft=systemd :
+[Unit]
+Description=Home Assistant
+
+[Service]
+Type=simple
+ExecStart=/usr/local/bin/hass
+User=homeassistant
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target