Clean Resolv.conf in official AMI build

1. Only cleanup resolv conf during official AMI build. In the future, we will evaluate to apply this improvement to all AMI builds.
2. Also clean up `/run/systemd/resolve/resolv.conf `. This file exists on Ubuntu

Signed-off-by: Hanwen <[email protected]>

Author: hanwen-cluster

cookbooks/aws-parallelcluster-platform/files/ami_cleanup.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+IS_OFFICIAL_AMI_BUILD=${1:-"false"}
+
 # clean up cloud init artifacts https://cloudinit.readthedocs.io/en/latest/topics/cli.html#clean
 cloud-init clean -s
 
@@ -21,8 +23,10 @@ if [ "${ID}${VERSION_ID}" == "centos7" ]; then
 fi
 
 # Clean resolv.conf if it's not managed by system
-if [ ! -L "/etc/resolv.conf" ]; then
-    sed -i '/^nameserver/d' /etc/resolv.conf
+if [ "${IS_OFFICIAL_AMI_BUILD}" == "true" ]; then
+    echo "Clean resolv.conf for official AMIs"
+    echo -n > /etc/resolv.conf
+    rm -f /run/systemd/resolve/resolv.conf
 fi
 
 find /var/log -type f -exec /bin/rm -v {} \;