Separate rsyslog image definition

This separates the rsyslog image definition into a server image
"rsyslog" and an "rsyslog-base" image. This will enable the creation of
more finegrained images depending on the use-case, e.g.: A minimal
side-car container image that merely outputs what it gets from syslog to
stdout.

Change-Id: I33ae15c0beb5af6179a84f3722150a287316ad25

docker/rsyslog/rsyslog-base/Dockerfile.j2

@@ -0,0 +1,15 @@
+FROM {{ namespace }}/{{ image_prefix }}base:{{ tag }}
+LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
+
+{% block rsyslog_base_header %}{% endblock %}
+
+{% import "macros.j2" as macros with context %}
+
+{% set rsyslog_base_packages = [
+    'rsyslog'
+] %}
+
+{{ macros.install_packages(rsyslog_base_packages | customizable("packages")) }}
+
+{% block rsyslog_base_footer %}{% endblock %}
+{% block footer %}{% endblock %}

docker/rsyslog/rsyslog/Dockerfile.j2

@@ -1,4 +1,4 @@
-FROM {{ namespace }}/{{ image_prefix }}base:{{ tag }}
+FROM {{ namespace }}/{{ image_prefix }}rsyslog-base:{{ tag }}
 LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
 
 {% block rsyslog_header %}{% endblock %}
@@ -7,15 +7,13 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
 
 {% if base_distro in ['centos', 'oraclelinux', 'rhel'] %}
     {% set rsyslog_packages = [
-            'rsyslog',
-            'rsyslog-gnutls',
-            'rsyslog-mmjsonparse',
-            'rsyslog-mmnormalize',
+        'rsyslog-gnutls',
+        'rsyslog-mmjsonparse',
+        'rsyslog-mmnormalize'
     ] %}
 {% elif base_distro in ['debian', 'ubuntu'] %}
     {% set rsyslog_packages = [
-            'rsyslog',
-            'rsyslog-gnutls',
+        'rsyslog-gnutls'
     ] %}
 {% endif %}