Make pull request BWC testing a matrix job for better parallelization

.ci/jobs.t/elastic+elasticsearch+pull-request+bwc.yml → .ci/jobs.t/elastic+elasticsearch+pull-request+bwc-snapshots.yml

@@ -1,9 +1,11 @@
 ---
 - job:
-    name: "elastic+elasticsearch+pull-request+bwc"
+    name: "elastic+elasticsearch+pull-request+bwc-snapshots"
     display-name: "elastic / elasticsearch - pull request bwc"
     description: "Testing of Elasticsearch pull requests - bwc"
-    workspace: "/dev/shm/elastic+elasticsearch+pull-request+bwc"
+    project-type: matrix
+    node: master
+    child-workspace: "/dev/shm/elastic+elasticsearch+pull-request+bwc"
     scm:
       - git:
           refspec: "+refs/pull/${ghprbPullId}/*:refs/remotes/origin/pr/${ghprbPullId}/*"
@@ -23,6 +25,16 @@
           black-list-labels:
             - '>test-mute'
             - 'test-full-bwc'
+    axes:
+      - axis:
+          type: slave
+          name: nodes
+          values:
+            - "general-purpose"
+      - axis:
+          type: yaml
+          filename: ".ci/snapshotBwcVersions"
+          name: "BWC_VERSION"
     builders:
       - inject:
           properties-file: '.ci/java-versions.properties'
@@ -34,4 +46,4 @@
             JAVA16_HOME=$HOME/.java/openjdk16
       - shell: |
           #!/usr/local/bin/runbld --redirect-stderr
-          $WORKSPACE/.ci/scripts/run-gradle.sh -Dignore.tests.seed bwcTestSnapshots
+          $WORKSPACE/.ci/scripts/run-gradle.sh -Dignore.tests.seed v$BWC_VERSION#bwcTest