Fix for error when Kraken is enabled
Fix for error when Kraken is enabled

When kraken is enabled, variable 'm' contains a list of species and contamination percentage, which would screw up the Pandas DataFrame conversion at line 187.
lbeltrame/bcbio-nextgen,mjafin/bcbio-nextgen,chapmanb/bcbio-nextgen,brainstorm/bcbio-nextgen,lbeltrame/bcbio-nextgen,vladsaveliev/bcbio-nextgen,mjafin/bcbio-nextgen,a113n/bcbio-nextgen,chapmanb/bcbio-nextgen,vladsaveliev/bcbio-nextgen,biocyberman/bcbio-nextgen,a113n/bcbio-nextgen,brainstorm/bcbio-nextgen,a113n/bcbio-nextgen,lbeltrame/bcbio-nextgen,vladsaveliev/bcbio-nextgen,brainstorm/bcbio-nextgen,biocyberman/bcbio-nextgen,chapmanb/bcbio-nextgen,mjafin/bcbio-nextgen,biocyberman/bcbio-nextgen