CNVkit: ensure we use configured TEMPDIR
CNVkit: ensure we use configured TEMPDIR

Avoids using global temporary directory for file write, which
causes issues on systems with restricted TMPDIRs. Thanks to @ohofmann

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