Set docker_prefix and manifest_docker_prefix correctly (#103)

Signed-off-by: Harshit Gupta <guptaharshit@microsoft.com>
Co-authored-by: Harshit Gupta <guptaharshit@microsoft.com>

Author: harshitgupta1337

kubevirtci/cluster-up/cluster/kind/common.sh

@@ -170,8 +170,8 @@ function prepare_config() {
 master_ip="127.0.0.1"
 kubeconfig=${BASE_PATH}/$KUBEVIRT_PROVIDER/.kubeconfig
 kubectl=${BASE_PATH}/$KUBEVIRT_PROVIDER/.kubectl
-docker_prefix=localhost:${HOST_PORT}/kubevirt
-manifest_docker_prefix=registry:5000/kubevirt
+docker_prefix=\${DOCKER_PREFIX:-localhost:${HOST_PORT}/kubevirt}
+manifest_docker_prefix=\${DOCKER_PREFIX:-registry:5000/kubevirt}
 EOF
 }