ci: move build scratch off node runtime storage

Jenkinsfile

@@ -1,11 +1,16 @@
 pipeline {
   agent {
     kubernetes {
+      // Keep build I/O off the node's runtime USB drive.
+      workspaceVolume dynamicPVC(accessModes: 'ReadWriteOnce', requestsSize: '40Gi', storageClassName: 'ci-scratch')
       defaultContainer 'tester'
       yaml """
 apiVersion: v1
 kind: Pod
 spec:
+  securityContext:
+    fsGroup: 1000
+    fsGroupChangePolicy: OnRootMismatch
   nodeSelector:
     kubernetes.io/arch: arm64
     node-role.kubernetes.io/worker: "true"
@@ -49,8 +54,9 @@ spec:
         - "--host=tcp://0.0.0.0:2375"
         - "--tls=false"
       volumeMounts:
-        - name: dind-storage
+        - name: workspace-volume
           mountPath: /var/lib/docker
+          subPath: .cache/docker
         - name: workspace-volume
           mountPath: /home/jenkins/agent
     - name: builder
@@ -89,20 +95,20 @@ spec:
   volumes:
     - name: docker-config-writable
       emptyDir: {}
-    - name: dind-storage
-      emptyDir: {}
     - name: harbor-config
       secret:
         secretName: harbor-robot-pipeline
         items:
           - key: .dockerconfigjson
             path: config.json
-    - name: workspace-volume
-      emptyDir: {}
 """
     }
   }
   environment {
+    PIP_CACHE_DIR = '/home/jenkins/agent/.cache/pip'
+    NPM_CONFIG_CACHE = '/home/jenkins/agent/.cache/npm'
+    SONAR_USER_HOME = '/home/jenkins/agent/.cache/sonar'
+    TMPDIR = '/home/jenkins/agent/.cache/tmp'
     PIP_DISABLE_PIP_VERSION_CHECK = '1'
     PYTHONUNBUFFERED = '1'
     SUITE_NAME = 'atlasbot'
@@ -118,6 +124,11 @@ spec:
     buildDiscarder(logRotator(daysToKeepStr: '30', numToKeepStr: '200', artifactDaysToKeepStr: '30', artifactNumToKeepStr: '120'))
   }
   stages {
+    stage('Prepare build scratch') {
+      steps {
+        sh 'mkdir -p /home/jenkins/agent/.cache/tmp /home/jenkins/agent/.cache/go-tmp'
+      }
+    }
     stage('Checkout') {
       steps {
         checkout scm