core: [cleanup] organize canMigrateVm method

This patch organize MigrateVmCommand#canMigrateVm method:
1. replaced the unused paramter vmGuid with VM instance. that way, the
method is more testable (can be tested without mocking, just insert a
different VM to check as parameter)
2. remove the can-do-action error messages list from the parameters, and
use addCanDoActionMessage & failCanDoAction methods inside the method
instead
3. set the action and type for the can-do-action messages in the
standard way by override setActionMessageParameters method

Change-Id: Ica36ecc272a295ee82ec51d7b62a90d84489d8c9
Signed-off-by: Arik Hadas <ahadas@redhat.com>