bnc#884615 VML import: import OLE objects in header with background wrapping

We already do this for drawingML shapes since commit
500343105707a9905f5198a4af6ad58fe307b7c2 (DOCX drawingML shape import:
always set Opaque, 2013-12-04), make the VML / OLE case behave the same
as well.

Change-Id: Ic22f1f3cfd325ccbbb9bd6fe9814553683e4de55