Avoid loading GTF database unless needed
Avoid loading GTF database unless needed

Tries to work around sqlite3 connection errors in #1123 if
the BED file was pre-created during installation.

chapmanb/bcbio-nextgen,biocyberman/bcbio-nextgen,brainstorm/bcbio-nextgen,lpantano/bcbio-nextgen,lbeltrame/bcbio-nextgen,a113n/bcbio-nextgen,biocyberman/bcbio-nextgen,vladsaveliev/bcbio-nextgen,biocyberman/bcbio-nextgen,lpantano/bcbio-nextgen,lpantano/bcbio-nextgen,a113n/bcbio-nextgen,a113n/bcbio-nextgen,Cyberbio-Lab/bcbio-nextgen,chapmanb/bcbio-nextgen,gifford-lab/bcbio-nextgen,gifford-lab/bcbio-nextgen,gifford-lab/bcbio-nextgen,mjafin/bcbio-nextgen,lbeltrame/bcbio-nextgen,Cyberbio-Lab/bcbio-nextgen,vladsaveliev/bcbio-nextgen,brainstorm/bcbio-nextgen,vladsaveliev/bcbio-nextgen,Cyberbio-Lab/bcbio-nextgen,lbeltrame/bcbio-nextgen,chapmanb/bcbio-nextgen,mjafin/bcbio-nextgen,brainstorm/bcbio-nextgen,mjafin/bcbio-nextgen