statistics.py: add %-lts suite variant
statistics.py: add %-lts suite variant

needed to support LTS in statistics

see: #761111

nonas/debian-qa,sophiejjj/debsources,oorestisime/debsources,oorestisime/debsources,matthieucan/debsources,zacchiro/debsources,nonas/debian-qa,vivekanand1101/debsources,vivekanand1101/debsources,devoxel/debsources,Debian/debsources,matthieucan/debsources,clemux/debsources,vivekanand1101/debsources,Debian/debsources,nonas/debian-qa,Debian/debsources,clemux/debsources,devoxel/debsources,nonas/debian-qa,devoxel/debsources,devoxel/debsources,oorestisime/debsources,clemux/debsources,zacchiro/debsources,zacchiro/debsources,sophiejjj/debsources,sophiejjj/debsources,matthieucan/debsources,vivekanand1101/debsources,devoxel/debsources,clemux/debsources,matthieucan/debsources,Debian/debsources,matthieucan/debsources,oorestisime/debsources,oorestisime/debsources,zacchiro/debsources,clemux/debsources,sophiejjj/debsources,zacchiro/debsources,sophiejjj/debsources,Debian/debsources,vivekanand1101/debsources