Permit changing yum configuration in the base image

This commit allows to configure yum settings via a yum.conf file that
is shipped in the base image and make it overridable with the
base_yum_conf jinja2 block.

Change-Id: I76a84ec008fec5696cadefdbdeb4204a32421c4b
Closes-Bug: #1698134

docker/base/Dockerfile.j2

@@ -40,6 +40,10 @@ RUN CURRENT_DISTRO_RELEASE=$(awk '{match($0, /[0-9]+/,version)}END{print version
     && cat /tmp/kolla_bashrc >> /etc/bashrc \
     && sed -i 's|^\(override_install_langs=.*\)|# \1|' /etc/yum.conf
 
+{% block base_yum_conf %}
+COPY yum.conf /etc/yum.conf
+{% endblock %}
+
 #### BEGIN REPO ENABLEMENT
 {% set base_yum_repo_files = [
  ] %}

docker/base/yum.conf

@@ -0,0 +1,9 @@
+[main]
+keepcache=0
+logfile=/var/log/yum.log
+exactarch=1
+obsoletes=1
+gpgcheck=1
+plugins=1
+installonly_limit=0
+skip_missing_names_on_install=False

docker/macros.j2

@@ -1,7 +1,7 @@
 {% macro install_packages(packages) -%}
 {% if packages is defined and packages|length > 0 -%}
     {% if base_distro in ['centos', 'oraclelinux', 'rhel'] -%}
-        RUN yum --setopt skip_missing_names_on_install=False -y install {{ packages | join(' ') }} && yum clean all
+        RUN yum -y install {{ packages | join(' ') }} && yum clean all
     {%- elif base_distro in ['debian', 'ubuntu'] -%}
         {#-
           debian_package_install is a utility method to build up an appropriate

releasenotes/notes/yum_conf-36fef802e8c003f1.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - Allow to configure yum settings, and provide a default yum.conf that is
+    overridable via the base_yum_conf jinja2 block.