Respect DISPLAY_SKIPPED_HOSTS when play doesn't match any hosts

When running a playbook where certain plays have no matching hosts, a 'skipped' message is displayed:

```
PLAY [deploy service] *************************************** 
skipping: no hosts matched

PLAY [deploy pres] *************************************************** 
skipping: no hosts matched
```

This patch makes this message respecting 'constants.DISPLAY_SKIPPED_HOSTS`:

```
PLAY [deploy service] *************************************** 

PLAY [deploy pres] *************************************************** 
```