[9.1] [ci] Move java paths (#229894) (#231724)

# Backport

This will backport the following commits from `main` to `9.1`:
- [[ci] Move java paths
(#229894)](#229894)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT
[{"author":{"name":"Jon","email":"[email protected]"},"sourceCommit":{"committedDate":"2025-08-14T01:14:32Z","message":"[ci]
Move java paths (#229894)\n\nInstead of manually managing various java
versions, this moves to\nreferencing apt managed installations.\n\nThese
are currently used for bazel and building elasticsearch.\n\nTested
at\nhttps://buildkite.com/elastic/kibana-elasticsearch-snapshot-build/builds/6526","sha":"5245f408a88467a3486488357685b183d02565d8","branchLabelMapping":{"^v9.2.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Operations","release_note:skip","skip-ci","backport:all-open","v9.2.0"],"title":"[ci]
Move java
paths","number":229894,"url":"https://github.com/elastic/kibana/pull/229894","mergeCommit":{"message":"[ci]
Move java paths (#229894)\n\nInstead of manually managing various java
versions, this moves to\nreferencing apt managed installations.\n\nThese
are currently used for bazel and building elasticsearch.\n\nTested
at\nhttps://buildkite.com/elastic/kibana-elasticsearch-snapshot-build/builds/6526","sha":"5245f408a88467a3486488357685b183d02565d8"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.2.0","branchLabelMappingKey":"^v9.2.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/229894","number":229894,"mergeCommit":{"message":"[ci]
Move java paths (#229894)\n\nInstead of manually managing various java
versions, this moves to\nreferencing apt managed installations.\n\nThese
are currently used for bazel and building elasticsearch.\n\nTested
at\nhttps://buildkite.com/elastic/kibana-elasticsearch-snapshot-build/builds/6526","sha":"5245f408a88467a3486488357685b183d02565d8"}}]}]
BACKPORT-->

Co-authored-by: Jon <[email protected]>

Author: kibanamachine

.buildkite/scripts/steps/es_snapshots/build.sh

@@ -35,11 +35,19 @@ export BUILD_URL=""
 export JOB_NAME=""
 export NODE_NAME=""
 
-# Reads the ES_BUILD_JAVA env var out of .ci/java-versions.properties and exports it
-export "$(grep '^ES_BUILD_JAVA' .ci/java-versions.properties | xargs)"
+export JAVA_VERSION="$(grep '^ES_BUILD_JAVA' .ci/java-versions.properties | sed 's/ES_BUILD_JAVA=openjdk//')"
+if [[ -z "$JAVA_VERSION" ]]; then
+  echo "No ES_BUILD_JAVA version found."
+  exit 1
+fi
+
+export JAVA_HOME=$(update-alternatives --list java | grep "java-$JAVA_VERSION-openjdk" | sed 's#/bin/java$##')
+if [[ -z "$JAVA_HOME" ]]; then
+  echo "No compatible JDK found.  Ensure openjdk-$JAVA_VERSION is installed."
+  exit 1
+fi
 
-export PATH="$HOME/.java/$ES_BUILD_JAVA/bin:$PATH"
-export JAVA_HOME="$HOME/.java/$ES_BUILD_JAVA"
+export PATH="$JAVA_HOME/bin:$PATH"
 export DOCKER_BUILDKIT=1
 
 # The Elasticsearch Dockerfile needs to be built with root privileges, but Docker on our servers is running using a non-root user