GATK4: turn off HaplotypeCallerSpark
GATK4: turn off HaplotypeCallerSpark

Use multicore HaplotypeCaller runs instead of Spark implementation
pending GATK fixes: broadinstitute/gatk#3725 broadinstitute/gatk#3659

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