export GCE_SERVICE_ACCOUNT in e2e.sh

hack/jenkins/e2e.sh

@@ -1080,6 +1080,7 @@ export KUBE_GCS_STAGING_PATH_SUFFIX=${KUBE_GCS_STAGING_PATH_SUFFIX:-}
 export KUBE_GCE_NODE_PROJECT=${KUBE_GCE_NODE_PROJECT:-}
 export KUBE_GCE_NODE_IMAGE=${KUBE_GCE_NODE_IMAGE:-}
 export KUBE_OS_DISTRIBUTION=${KUBE_OS_DISTRIBUTION:-}
+export GCE_SERVICE_ACCOUNT=${GCE_SERVICE_ACCOUNT:-}
 
 # GKE variables
 export CLUSTER_NAME=${E2E_CLUSTER_NAME}