Stop "dnf makecache" in the amphora images

On base operating systems that use DNF there can be a systemd timer
that attempts to call out and update the dnf cache every hour.
This patch adds an diskimage-builder element that disables this
timer as most amphora will not be successful in updating this cache
because they do not have network access or DNS services avaialable.

Change-Id: I5dec631d3e66e1dfb6b8741caea89938ee18a7d8
Story: 2007408
Task: 39019

diskimage-create/diskimage-create.sh

@@ -444,6 +444,11 @@ if [ "$AMP_ENABLE_FULL_MAC_SECURITY" -ne 1 ]; then
     fi
 fi
 
+# Disable the dnf makecache timer
+if [ "${AMP_BASEOS}" = "centos-minimal" ] || [ "${AMP_BASEOS}" = "fedora" ] || [ "${AMP_BASEOS}" = "rhel" ]; then
+    AMP_element_sequence="$AMP_element_sequence disable-makecache"
+fi
+
 if [ "${AMP_BASEOS}" = "centos-minimal" ]; then
     export DIB_YUM_MINIMAL_CREATE_INTERFACES=0
 fi

elements/disable-makecache/README.rst

@@ -0,0 +1,6 @@
+This element disables the dnf makecache hourly timer.
+
+The amphora typically do not have internet access nor access to DNS servers.
+We want to disable this makecache timer to stop the amphora from attempting
+to update/download the dnf cache every hour. Without this element it will
+run and log a failure every hour.

elements/disable-makecache/post-install.d/80-disable-makecache

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
+    set -x
+fi
+
+set -eu
+set -o pipefail
+
+case $DISTRO_NAME in
+    fedora | centos* | rhel* )
+        systemctl disable dnf-makecache.timer || true
+    ;;
+    *)
+        echo "ERROR: Unsupported distribution $DISTRO_NAME"
+        exit 1
+    ;;
+esac

elements/disable-makecache/svc-map

@@ -0,0 +1,2 @@
+disable-makecache:
+  default: disable-makecache