Add ability to specify filesystem type

[ricardorg79]

Right now ext4 is hardcoded. We need to add the ability to specify other filesystems when creating volumes.

[displague]

XFS, BTRFS, and Ext(2-4) are now available with the volume create option "filesystem"

https://github.com/linode/docker-volume-linode#create-options