webadmin: fix Save Memory visibility on create snapshot

Create Snapshot dialog:
'Save Memory' checkbox should be visible only when VM is running.

Following the fix in change I21de53a8f9092085beee28124ef2321538e76669,
setVm should be invoked after setWindow (as VM PropertyChangedEvent
listener is added on edit method of VmSnapshotCreatePopupWidget).

Change-Id: I732132f1f9132e47451fcf02e793d0a2ffc6d11f
Bug-Url: https://bugzilla.redhat.com/1056651
Signed-off-by: Daniel Erez <derez@redhat.com>