Fixed missing import of bio.structrural.shared
Fixed missing import of bio.structrural.shared

Line 131 in cnvkit.py calls shared.find_case_control() but `shared` module was
not imported.

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