Fix jib-gradle task

This wil fix the issue jib gradle task
gettng failed on security constrained
environments like OpenShift

Fix tektoncd#198

Author: piyush-garg

jib-gradle/jib-gradle.yaml

@@ -42,6 +42,7 @@ spec:
       # Runs the Gradle Jib build.
       gradle jib \
         --stacktrace --console=plain \
+        -g gradle-user-home \
         --init-script=/tekton/home/init-script.gradle \
         -Duser.home=/tekton/home \
         -Dgradle.user.home=/tekton/home/.gradle \