Avoid redeclaration errors for kube-up.sh

cluster/kube-env.sh

@@ -23,9 +23,10 @@
 KUBERNETES_PROVIDER=${KUBERNETES_PROVIDER:-gce}
 
 # Some useful colors.
-declare -r color_start="\033["
-declare -r color_red="${color_start}0;31m"
-declare -r color_yellow="${color_start}0;33m"
-declare -r color_green="${color_start}0;32m"
-declare -r color_norm="${color_start}0m"
-
+if [[ -z "${color_start-}" ]]; then
+  declare -r color_start="\033["
+  declare -r color_red="${color_start}0;31m"
+  declare -r color_yellow="${color_start}0;33m"
+  declare -r color_green="${color_start}0;32m"
+  declare -r color_norm="${color_start}0m"
+fi