vz: fixes: snapshot: Factor out virDomainMomentDef class
Fix for commit ffc0fbebe refactoring snapshot code.
Reviewed-by: Cole Robinson <crobinso@redhat.com>
ACKed-by: Maxim Nestratov <mnestratov@virtuozzo.com>
Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>