Update _vgmerge_single() to move fid->metadata_areas_ignored.

Update _vgmerge_single() to move fid->metadata_areas_ignored.

When vgmerge is called we move the mdas from the source to the
destination.  With metadata balancing we now have another mda
list, fid->metadata_areas_ignored, so move the mdas on this list
as well.

This patch should not matter as the code is written today.  However
we include it for completeness in the case that _vgmerge_single()
is refactored and/or moved into a library function.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>