Add support for file system type and label for volumes

[andrewsomething]

Block storage volumes allow for setting a file system type and label on creation. Specifying a file system type leads to a better user experience. Without that, the resulting volume is just a raw block device you need to mount and format. If you specify a file system type, it is preformatted and will be automatically mounted it when connected to a Droplet.

See: https://developers.digitalocean.com/documentation/v2/#block-storage