Fix: Remove stale Packer nameserver in RHEL-based images on OpenStack

Adds a final shell provisioner at the end of the build to remove all
'nameserver' entries from /etc/resolv.conf before finalizing RHEL-based
images. This addresses a bug where RHEL/NetworkManager retains the
temporary Packer build subnet nameserver (e.g., 10.0.2.3) alongside
DHCP-provided ones, causing intermittent DNS resolution failures for
internal domains in OpenStack.

Implementation details:
- A variable is introduced in packer.json.tmpl (default: false).
- This variable is overridden to true in qemu-rockylinux-9.json so the
  cleanup runs for all RHEL-based images.
- Non-RHEL builds remain unaffected.

Placed after Goss validation so:
- Goss runs with working DNS during build
- Final image boots with only DHCP-provided nameservers
- Cloud-init does not reintroduce stale nameservers

Fixes #1832

Signed-off-by: Truong Hoang Phu Loc <[email protected]>

Author: TruongHoangPhuLoc

images/capi/packer/qemu/packer.json.tmpl

@@ -152,6 +152,23 @@
         "kubernetes_version": "{{user `kubernetes_semver` | replace \"v\" \"\" 1}}"
       },
       "version": "{{user `goss_version`}}"
+    },      
+    {
+        "type": "shell",
+        "environment_vars": [
+          "REMOVE_NAMESERVER={{user `remove_nameserver`}}"
+        ],
+        "inline": [
+          "if [ \"$REMOVE_NAMESERVER\" = \"true\" ]; then",
+          "  cat /etc/resolv.conf",
+          "  echo 'Removing nameserver from resolv.conf...'",
+          "  sudo sed -i '/^nameserver/d' /etc/resolv.conf",
+          "  echo 'Removing stale nameserver is done, checking the current content of /etc/resolv.conf...'",
+          "  cat /etc/resolv.conf",
+          "else",
+          "  echo 'Skipping nameserver cleanup.'",
+          "fi"
+        ]
     }
   ],
   "variables": {

images/capi/packer/qemu/qemu-rockylinux-9.json

@@ -13,5 +13,6 @@
   "iso_url": "https://dl.rockylinux.org/vault/rocky/9.4/isos/x86_64/Rocky-9.4-x86_64-minimal.iso",
   "os_display_name": "RockyLinux 9",
   "redhat_epel_rpm": "https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm",
+  "remove_nameserver": "true",
   "shutdown_command": "/sbin/halt -h -p"
 }