seq2c: improve combined sanity check to handle shared normals
seq2c: improve combined sanity check to handle shared normals

These will have multiple identical coverage files due to the batching.

lbeltrame/bcbio-nextgen,lbeltrame/bcbio-nextgen,chapmanb/bcbio-nextgen,vladsaveliev/bcbio-nextgen,chapmanb/bcbio-nextgen,a113n/bcbio-nextgen,vladsaveliev/bcbio-nextgen,chapmanb/bcbio-nextgen,a113n/bcbio-nextgen,lbeltrame/bcbio-nextgen,vladsaveliev/bcbio-nextgen,a113n/bcbio-nextgen