Pass stageName to dockerExecuteOnKubernetes (#1162)

This fixes configuring sidecars for the given stage when Jenkins runs
on Kubernetes and the surounding stage has passed a stageName via parameters which is different from env.STAGE_NAME.

vars/piperStageWrapper.groovy

@@ -34,7 +34,7 @@ void call(Map parameters = [:], body) {
             if (Boolean.valueOf(env.ON_K8S) && containerMap.size() > 0) {
                 DebugReport.instance.environment.put("environment", "Kubernetes")
                 withEnv(["POD_NAME=${stageName}"]) {
-                    dockerExecuteOnKubernetes(script: script, containerMap: containerMap) {
+                    dockerExecuteOnKubernetes(script: script, containerMap: containerMap, stageName: stageName) {
                         executeStage(script, body, stageName, config, utils)
                     }
                 }