core: RemoveVdsCommandTest - proper setup

Fixed several set up issues in this test:
* Using MockitoRunner instead of calling the annotation
  initialization explicitly.
* Having a different GUID each test instead of a constant
* Stop hiding the command member

Change-Id: I03f327f958506016a561e26df5a949aab306c266
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: RemoveVdsCommandTest +  CanDoActionTestUtils

Use CanDoActionTestUtils in RemoveVdsCommandTest instead of
reinventing the wheel.

Change-Id: I946881b0cc7cdad1293b27517a04a624231b9563
Signed-off-by: Allon Mureinik <amureini@redhat.com>