Add env variable to tests/Dockerfile for gitops tests

Change-Id: I769775d8b40206f22f073a5fae0d051b774d4572
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/docker/tests/Dockerfile b/docker/tests/Dockerfile
index de90061..95248f1 100644
--- a/docker/tests/Dockerfile
+++ b/docker/tests/Dockerfile
@@ -108,6 +108,9 @@
 # Kubeconfig file
 ENV K8S_CREDENTIALS=/root/.kube/config
 
+# Kubeconfig file of the existing cluster for Gitops tests
+ENV CLUSTER_KUBECONFIG_CREDENTIALS=/robot-systest/cluster-kubeconfig.yaml
+
 # OSM RSA file
 ENV OSM_RSA_FILE=/root/osm_id_rsa