enable python 3 testing for debtcollector
enable python 3 testing for debtcollector

The debtcollector library should be tested under python 3.

Change-Id: Ic2de2da0a9b6535bcdad085fa745ae72f9cfcb23

anbangr/osci-project-config,open-switch/infra_project-config,citrix-openstack/project-config,dongwenjuan/project-config,openstack-infra/project-config,dongwenjuan/project-config,Tesora/tesora-project-config,coolsvap/project-config,openstack-infra/project-config,noorul/os-project-config,noorul/os-project-config,Tesora/tesora-project-config,coolsvap/project-config,anbangr/osci-project-config,citrix-openstack/project-config,open-switch/infra_project-config