svtk vcfcluster creates lists of INFO values when Number = 1

[epiercehoffman]

When svtk vcfcluster merges records, it creates lists of INFO values from the member records, even when the Number for the INFO key defined in the header is 1 (link). This can create issues down the line when the INFO values don't match the Number, so this behavior should be fixed.

[mwalker174]

I think the best options are:

1. Choose a representative record and fill unrecognized fields with that or
2. Use empty value .

The latter is a bit "safer" in terms of possibly propagating bad information. This issue could take significant time/testing to ensure it doesn't cause any issues downstream of CombineBatches.