Add disks to LVM pool: control and model changes

Added a new update parameter to storagepool resource. Changed the
logic in the model to accept any update parameter ('autostart' or
'disks'). 'disks' parameter will add disks/partitions to the
target LVM pool.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Add disks to LVM pool: API.md changes

Adding documentation about the new 'disks' update parameter,
pool type 'logical' only.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Add disks to LVM pool: mockmodel changes

Eliminated the parameter validation that is now being done
in API.json.

To simulate the operation of add disks in the mockmodel, for
each disk (which is validated with real data from the host),
for each new disk added a fixed amount is added in the
'capacity' and 'available' fields on the pool.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Add disks to LVM pool: API.json changes

This patch adds a new section 'storagepool_update' in API.json
in order to remove parameter validation inside the model.

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