Fix single-version-externally-mananged typo in setup.cfg
Fix single-version-externally-mananged typo in setup.cfg

Corrects the typo in setup.cfg to use single-version-externally-managed
for pbr.

Fixes bug 1192987

Change-Id: I039b51897ec180148e5095349e4567759f2711a5

openstack/networking-odl,citrix-openstack-build/neutron-fwaas,FedericoRessi/networking-odl,CiscoSystems/networking-odl,gaolichuang/neutron-fwaas,mestery/x-stackforge-odl,openstack/neutron-fwaas,gaolichuang/neutron-fwaas,FedericoRessi/networking-odl,flavio-fernandes/networking-odl,openstack/neutron-fwaas,flavio-fernandes/networking-odl,citrix-openstack-build/neutron-vpnaas,openstack/neutron-vpnaas,openstack/networking-odl,openstack/networking-odl,schoksey/networking-odl,schoksey/networking-odl,dougwig/x-neutron-vpnaas,CiscoSystems/networking-odl,openstack/neutron-vpnaas,dougwig/x-neutron-fwaas