Fix issue #339: Enable backend to handle not persistent pools

This patch changes the error message when storage pool is not found and
adds the isPersistent checkings, in order to return correctly from
deactivate function.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix issue #339: Changes UI to handle deactivation of non-persistent pools

This patch implements a checking in the UI in order to warn the user
that if pool is not persistent it will be removed when deactivated.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix issue #339: Change mock and add test to check persistent variable

This patch fixes the problems in the tests due to the inclusion of new
persistent variable in pools information. It also adds a minor test.

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