Update motd.sls

This patch unifies /etc/motd managing approach for both RedHat and
Ubuntu systems. Providing a string value via linux:system:motd
pillar will configure static /etc/motd and remove dynamic scripts
from /etc/update-motd.d (if present).

update-motd can safely be removed because Ubuntu supports dynamic
motd by pam_motd means since 2009.

Related-Prod: PROD-17287

Change-Id: Ic9b7e18abb12cfe8704717b14dc1237e40715319

README.rst

@@ -825,9 +825,28 @@ default).
 Message of the day
 ~~~~~~~~~~~~~~~~~~
 
-``pam_motd`` from package ``update-motd`` is used for dynamic messages of the
+``pam_motd`` from package ``libpam-modules`` is used for dynamic messages of the
 day. Setting custom motd will cleanup existing ones.
 
+Setting static motd will replace existing ``/etc/motd`` and remove scripts from
+``/etc/update-motd.d``.
+
+Setting static motd:
+
+.. code-block:: yaml
+
+    linux:
+      system:
+        motd: |
+          UNAUTHORIZED ACCESS TO THIS SYSTEM IS PROHIBITED
+
+          You must have explicit, authorized permission to access or configure this
+          device. Unauthorized attempts and actions to access or use this system may
+          result in civil and/or criminal penalties.
+          All activities performed on this system are logged and monitored.
+
+Setting dynamic motd:
+
 .. code-block:: yaml
 
     linux:

linux/system/motd.sls

@@ -1,27 +1,19 @@
 {%- from "linux/map.jinja" import system with context %}
-{%- if system.enabled %}
+{%- if system.enabled and system.motd|length > 0 %}
 
-{%- if grains.os_family == 'RedHat' %}
+/etc/update-motd.d:
+  file.directory:
+    - clean: true
 
-{#- update-motd is not available in RedHat, so support only static motd #}
+{%- if system.motd is string %}
+
+{#- Set static motd only #}
 /etc/motd:
   file.managed:
     - contents_pillar: linux:system:motd
 
 {%- else %}
 
-{%- if grains.os == 'Ubuntu' %}
-package_update_motd:
-  pkg.installed:
-    - name: update-motd
-    - require_in:
-      - file: /etc/update-motd.d
-{%- endif %}
-
-/etc/update-motd.d:
-  file.directory:
-    - clean: true
-
 {%- if grains.oscodename == "jessie" %}
 motd_fix_pam_sshd:
   file.replace: