Add ChangeMachineId configuration task

This task is used when deploying Linux instances to alter the
content of `/etc/machine-id`. This file contains an ID that is supposed
to be globally unique. When deploying an image it is better to
regenerate a random new one to assure the uniqueness. For more info
check:

https://www.freedesktop.org/software/systemd/man/machine-id.html

docs/architecture.rst

@@ -173,6 +173,11 @@ SUSE and Gentoo derived distributions. The hostname is read from
 *SNF_IMAGE_HOSTNAME* variable. In addition to the latter, *SNF_IMAGE_TARGET* is
 also required.
 
+**ChangeMachineId**: On Linux instances, this script will generate a new random
+machine ID and will place it in ``/etc/machine-id``. For more info check
+`here <https://www.freedesktop.org/software/systemd/man/machine-id.html>`_. The
+task will fail if *SNF_IMAGE_TARGET* is missing.
+
 **ChangePassword**: Changes the password for a list of existing users. On Linux 
 systems this is accomplished by directly altering the instance's
 ``/etc/shadow`` file. On Windows systems a script is injected into the VM's
@@ -257,6 +262,8 @@ property must be defined.
 |AssignHostname                 |50 |InstallUnattend   |EnforcePersonality       |TARGET                   |                           |
 |                               |   |                  |                         |HOSTNAME                 |PROPERTY_OSFAMILY          |
 +-------------------------------+---+------------------+-------------------------+-------------------------+---------------------------+
+|ChangeMachineId                |50 |InstallUnattend   |EnforcePersonality       |TARGET                   |PROPERTY_OSFAMILY          |
++-------------------------------+---+------------------+-------------------------+-------------------------+---------------------------+
 |ChangePassword                 |50 |InstallUnattend   |EnforcePersonality       |TARGET                   |PROPERTY_USERS             |
 |                               |   |                  |                         |                         |PROPERTY_OSFAMILY          |
 |                               |   |                  |                         |                         |PASSWD                     |

snf-image-helper/tasks/50ChangeMachineId.in

+#! /bin/bash
+
+# Copyright (C) 2016 GRNET S.A.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+### BEGIN TASK INFO
+# Provides:		ClearMachineId
+# RunBefore:            EnforcePersonality
+# RunAfter:             FilesystemResizeMounted
+# Short-Description:    Regenerate /etc/machine-id file in Linux Systems
+### END TASK INFO
+
+set -e
+. "@commondir@/common.sh"
+
+trap task_cleanup EXIT
+report_task_start
+
+# Check if the task should be prevented from running.
+check_if_excluded
+check_if_mounted_excluded
+
+if [ ! -d "$SNF_IMAGE_TARGET" ]; then
+    log_error "Target dir: \`$SNF_IMAGE_TARGET' is missing."
+fi
+
+# Check if the image overwrites the task
+check_if_overwritten
+
+if [ "$SNF_IMAGE_PROPERTY_OSFAMILY" != "linux" ]; then
+    exit 0
+fi
+
+# Generate a new random UUID
+uuid=$(sed 's/-//g' /proc/sys/kernel/random/uuid)
+
+if [ -f "$SNF_IMAGE_TARGET/etc/machine-id" ]; then
+    echo "$uuid" > "$SNF_IMAGE_TARGET/etc/machine-id"
+else
+    warn "\`/etc/machine-id' file is not present"
+fi
+
+# The machine-id may be also cached by dbus
+if [ -f "$SNF_IMAGE_TARGET/var/lib/dbus/machine-id" ]; then
+    echo "$uuid" > "$SNF_IMAGE_TARGET/var/lib/dbus/machine-id"
+else
+    warn "\`/var/lib/dbus/machine-id' file is not present"
+fi
+
+exit 0
+
+# vim: set sta sts=4 shiftwidth=4 sw=4 et ai :

snf-image-helper/tasks/Makefile.am

@@ -8,6 +8,7 @@ dist_tasks_SCRIPTS = \
 		40FilesystemResizeMounted \
 		50AddSwap \
 		50AssignHostname \
+		50ChangeMachineId \
 		50ChangePassword \
 		50ConfigureNetwork \
 		50DeleteSSHKeys \