Check for certain vg_read errors in _process_one_vg iterator.
In _process_one_vg, we should never proceed if the VG read fails with certain
conditions. If we cannot allocate or construct the volume_group structure,
we should not proceed - this is true regardless of the tool calling the
iterator. In other cases, when the volume group structure is constructed but
there is some error (PVs missing, metadata corrupted, etc), some tools may
want to process the VG while others may not.