Add ntp to the servers so the times are up to date between them.

Found during deployment:

```
[2014-10-09 02:48:16]  ** [out :: 10.0.1.4] tar: 20141009014804/vendor/autoload.php: time stamp 2014-10-09 02:48:14 is 6.503790157 s in the future
```

Installing `ntp` updates the date and time on the VMs so they're synchronised properly.