add digitalocean v2 api support

This commit add v2 api support to digitalocean builder

Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>
In do examples i don't see floats, and they provide type number for it. As i know number int/uint.
```
transfer	number	The amount of transfer bandwidth that is available for Droplets created in this size. This only counts traffic on the public interface. The value is given in terabytes.
```