envns should be availabe in message line (#734)

This line warns the user that dependent environment doesn’t exist, and presents the command line
for creating an environment.

When the variable `envNamespace` is specified, the `envns` option should be available as well.

fission/function.go

@@ -180,7 +180,7 @@ func fnCreate(c *cli.Context) error {
 		})
 		if err != nil {
 			if e, ok := err.(fission.Error); ok && e.Code == fission.ErrorNotFound {
-				fmt.Printf("Environment \"%v\" does not exist. Please create the environment before executing the function. \nFor example: `fission env create --name %v --image <image>`\n", envName, envName)
+				fmt.Printf("Environment \"%v\" does not exist. Please create the environment before executing the function. \nFor example: `fission env create --name %v --envns %v --image <image>`\n", envName, envName, envNamespace)
 			} else {
 				checkErr(err, "retrieve environment information")
 			}