core: refactoring in UpdateVmVersionCommand

- extract parameters initialization to separate method
- rename removeVmFromPoolParas to removeVmFromPoolParams
- prevent possible NPE on getExclusiveLocks

Change-Id: Id9626104a21060dcef1a60beb1b83873037f779b
Signed-off-by: Arik Hadas <ahadas@redhat.com>