Fix initialization of docker proxy and registry vars in install_k3s_cluster.sh

Change-Id: I3adec3783af8dd89aa903d35ed624e9853beae27
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>

installers/install_k3s_cluster.sh

@@ -244,10 +244,10 @@ done
 DEBUG_INSTALL=${DEBUG_INSTALL:-}
 DEFAULT_IP=${DEFAULT_IP:-"127.0.0.1"}
 OSM_DEVOPS=${OSM_DEVOPS:-"/usr/share/osm-devops"}
-DOCKER_PROXY_URL=${DOCKER_PROXY_URL=-}
-DOCKER_REGISTRY_URL=${DOCKER_REGISTRY_URL=-}
-DOCKER_REGISTRY_USER=${DOCKER_REGISTRY_USER=-}
-DOCKER_REGISTRY_PASSWORD=${DOCKER_REGISTRY_PASSWORD=-}
+DOCKER_PROXY_URL=${DOCKER_PROXY_URL:-}
+DOCKER_REGISTRY_URL=${DOCKER_REGISTRY_URL:-}
+DOCKER_REGISTRY_USER=${DOCKER_REGISTRY_USER:-}
+DOCKER_REGISTRY_PASSWORD=${DOCKER_REGISTRY_PASSWORD:-}
 K3S_PUBLIC_IP=${K3S_PUBLIC_IP:-}
 echo "DEBUG_INSTALL=${DEBUG_INSTALL}"
 echo "DEFAULT_IP=${DEFAULT_IP}"