VM Edit CPU/Memory: (Backend) Changes API.md, API.json and i18n.py

This patch apply necessary changes in:
  - documentation (API.md): adds cpu and memory in update parameter
  - data validation (API.json: validate given cpu and memory numbers
  - error message (i18n.py): this new feature uses the same messages
    from Templates update, but a minor change was necessary in cpu text.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
VM Edit CPU/Memory: (Backend) Changes VM control and model

This patch changes vm control file in order to allow user to change cpus
and memory. It also changes vms model in order to change xml properly
and test if vm is running.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
VM Edit CPU/Memory: (Backend) Changes mockmodel and tests

This patch changes the mockmodel in order to allow update of vm cpu
and memory. It also implements new tests for the updates and errors.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>