Tests: avoid conda-4.6 which seems to be source of slow installs
Tests: avoid conda-4.6 which seems to be source of slow installs

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