Display "None" for on command line when no bindings found

Prior to deployment, wskdeploy displays the entities and bindings that will be used for deployment. However, if there are no bindings, the word "bindings:" appears but nothing after it.

for example, on a package:
```
Packages:
Name: validate
bindings:

* action: validate_singleline_params
bindings:
- param_simple_string : "foo"
- param_simple_integer_2 : 0
...
```

I propose that we display the keyword "None" (colorized in YELLOW) to indicate that the tool indeed found no bindings (positive feedback).