Pin pbr version to avoid docutils setup failure
Pin pbr version to avoid docutils setup failure

Change-Id: I1760969145d14de18987f135244887e8bf0c845f

mhharsh/stackalytics,mohitsethi/stackalytics,openstack/stackalytics,stackforge/stackalytics,dliu2015/stackalytics_zanata,Code-Fly/stackalytics,Solinea/stackalytics,mohitsethi/stackalytics,Mirantis/stackalytics,nihilifer/stackalytics,Code-Fly/stackalytics,openstack/stackalytics,0xf2/stackalytics,AlexanderYAPPO/stackalytics,AlexanderYAPPO/stackalytics,danielmellado/stackalytics,Code-Fly/stackalytics,stackforge/stackalytics,openstack/stackalytics,Solinea/stackalytics,danielmellado/stackalytics,Mirantis/stackalytics,dliu2015/stackalytics_zanata,Solinea/stackalytics,nihilifer/stackalytics,Mirantis/stackalytics,nihilifer/stackalytics,dliu2015/stackalytics_zanata,0xf2/stackalytics,0xf2/stackalytics,0xf2/stackalytics,mhharsh/stackalytics,mhharsh/stackalytics,openstack/stackalytics,danielmellado/stackalytics,AlexanderYAPPO/stackalytics,mohitsethi/stackalytics,stackforge/stackalytics