[CI] Build docker image during packer_cache (#82145)

.ci/build_docker.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+set -euo pipefail
+
+cd "$(dirname "${0}")"
+
+cp /usr/local/bin/runbld ./
+cp /usr/local/bin/bash_standard_lib.sh ./
+
+docker build -t kibana-ci -f ./Dockerfile .

.ci/packer_cache_for_branch.sh

@@ -53,6 +53,8 @@ tar -cf "$HOME/.kibana/bootstrap_cache/$branch.tar" \
 
 echo "created $HOME/.kibana/bootstrap_cache/$branch.tar"
 
+.ci/build_docker.sh
+
 if [[ "$branch" != "master" ]]; then
   rm --preserve-root -rf "$checkoutDir"
 fi

vars/kibanaPipeline.groovy

@@ -390,12 +390,7 @@ def scriptTaskDocker(description, script) {
 
 def buildDocker() {
   sh(
-    script: """
-      cp /usr/local/bin/runbld .ci/
-      cp /usr/local/bin/bash_standard_lib.sh .ci/
-      cd .ci
-      docker build -t kibana-ci -f ./Dockerfile .
-    """,
+    script: "./.ci/build_docker.sh",
     label: 'Build CI Docker image'
   )
 }