Unstash via Utils.unstash (#4381)

We should only unstash using the Utils class.
The Jenkins unstash step does not log which stash was unstashed.

test/groovy/DockerExecuteOnKubernetesTest.groovy

@@ -68,6 +68,17 @@ class DockerExecuteOnKubernetesTest extends BasePiperTest {
     def podSpec
     Map resources =  [:]
     List stashList = []
+    List unstashList = []
+    def utilsMock = newUtilsMock()
+
+    Utils newUtilsMock() {
+        def utilsMock = new Utils()
+        utilsMock.steps = [
+            unstash  : { m -> unstashList.add(m) }
+        ]
+        utilsMock.echo = { def m -> }
+        return utilsMock
+    }
 
     @Before
     void init() {
@@ -809,6 +820,18 @@ class DockerExecuteOnKubernetesTest extends BasePiperTest {
             hasEntry('excludes', 'container/exclude.test'))))
     }
 
+    @Test
+    void testUnstash() {
+        stepRule.step.dockerExecuteOnKubernetes(
+            script: nullScript,
+            juStabUtils: utilsMock,
+            dockerImage: 'maven:3.5-jdk-8-alpine',
+        ) {}
+        assertEquals(2, unstashList.size())
+        assertTrue(unstashList[0].startsWith('workspace-'))
+        assertTrue(unstashList[1].startsWith('container-'))
+    }
+
     @Test
     void testDockerExecuteWithVolumeProperties() {
         stepRule.step.dockerExecuteOnKubernetes(

vars/dockerExecuteOnKubernetes.groovy

@@ -346,7 +346,7 @@ void executeOnPod(Map config, utils, Closure body, Script script) {
         }
     } finally {
         if (config.containerName)
-            unstashWorkspace(config, 'container')
+            unstashWorkspace(config, utils, 'container')
     }
 }
 
@@ -454,9 +454,9 @@ private Map getSecurityContext(Map config) {
     return config.securityContext ?: config.jenkinsKubernetes.securityContext ?: [:]
 }
 
-private void unstashWorkspace(config, prefix) {
+private void unstashWorkspace(config, utils, prefix) {
     try {
-        unstash "${prefix}-${config.uniqueId}"
+        utils.unstash "${prefix}-${config.uniqueId}"
     } catch (AbortException | IOException e) {
         echo "${e.getMessage()}\n${e.getCause()}"
     } catch (Throwable e) {