Merge "Pre-install python3 for CentOS"

diskimage_builder/elements/yum/pre-install.d/00-1-centos-python3

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+# Ensure the python3 interpreter and YAML libraries are installed
+# early (even before package-installs, which is written in Python and
+# uses YAML).
+
+if [[ ${DISTRO_NAME} =~ (centos|rhel) && ${DIB_RELEASE} == 7 ]]; then
+    # Our package map and install stuff doesn't have a way to say
+    # "install this from EPEL".  So we hack in an install of it here
+    # from EPEL.  Nothing else should have installed EPEL at this
+    # early stage.
+    yum install -y python3 epel-release
+    yum install -y python36-PyYAML
+    yum remove -y epel-release
+elif [[ ${DISTRO_NAME} =~ (centos|rhel) && ${DIB_RELEASE} > 7 ]]; then
+    # For 8 and above ensure the "user" python3 package is installed
+    # so we have /usr/bin/python3 and pyyaml.
+    dnf install -y python3 python3-pyyaml
+fi