Logical StoragePool: adding disks.py module

This module contains functions to retrieve partition's data from
the host, using commands such as lsblk and blkid.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Logical StoragePool: changes in model and mockmodel

Adding methods to support the new resource and models implemented in controller.py.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Logical StoragePool: changes in controller.py

Adding a new Collection type (Partitions) and a new Resource type (Partition).

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Logical StoragePool: changes in API.md

Updating the storagepool_xml API and adding the API for /host/partitions.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>