Zpool module

Create and modify a Zpool.

This Pull Request is based on ansible/ansible#8205. I think it was lost when the Module Repos were reorganized.
I fixed some Errors and add a new Feature: Add new devices to an existing pool. This allows Pools with nested Raid Levels like Raid10 or Raid50. 
adding disk by `sdc`, etc is only recommended for test or development pools: http://zfsonlinux.org/faq.html#WhatDevNamesShouldIUseWhenCreatingMyPool