!2539 bug fix: Isula ps not display N/A when ports empty

From: @wu-jichao123 
Reviewed-by: @xuxuepeng, @liuxu180400617, @taotao-sauce 
Signed-off-by: @taotao-sauce

src/cmd/isula/information/ps.c

@@ -332,7 +332,7 @@ static void print_basic_container_info_item(const struct isula_container_summary
     } else if (strcmp(name, "Created") == 0) {
         print_created_field(in->created, length->created_length);
     } else if (strcmp(name, "Ports") == 0) {
-        const char *ports = (in->ports != NULL ? in->ports : "N/A");
+        const char *ports = (in->ports != NULL ? in->ports : "     ");
         printf("%-*s", (int)length->ports_length, ports);
     }
 }