engine: Add created_by_user_id field to vm_static

Added created_by_user_id field to vm_static
and createdByUserId property to VmBase representing UUID
of the user who created the VM/Template.

This field is set on AddVmCommand and AddVmTemplateCommand.

Change-Id: I465f9c49d05f49d42814cd970c3df1ed763a7fb5
Signed-off-by: Martin Betak <mbetak@redhat.com>