Run jib-gradle as root

This will fix the issue of task not
working on OpenShift as it needs root access and
by default on OpenShift pod run as nonroot

Fix #198

(cherry picked from commit 46bdfaf5aa)

jib-gradle/jib-gradle.yaml

@@ -59,6 +59,8 @@ spec:
     - name: $(params.CACHE)
       mountPath: /tekton/home/.cache
       subPath: jib-cache
+    securityContext:
+      runAsUser: 0
 
   volumes:
   - name: empty-dir-volume