fix: use homopolymer-pair-HMM-mode of Varlociraptor in case of nanopore reads

[johanneskoester]

nanopore suffers from homopolymer errors. Varlociraptor can deal with them by having additional states in its pairHMM used for realignment of reads against considered alleles. This mode has to be explicitly activated whenever we process a nanopore sample.

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