prepare-build-env.sh: add missing dependencies
prepare-build-env.sh: add missing dependencies

pbr is required in order to build fuel-agent

Closes-bug: #1372008

Change-Id: Ib493cecb71e7b95433599a4598c61a7975ba9923

SmartInfrastructures/fuel-main-dev,AnselZhangGit/fuel-main,AnselZhangGit/fuel-main,eayunstack/fuel-main,ddepaoli3/fuel-main-dev,dancn/fuel-main-dev,Fiware/ops.Fuel-main-dev,SergK/fuel-main,Fiware/ops.Fuel-main-dev,AnselZhangGit/fuel-main,teselkin/fuel-main,zhaochao/fuel-main,dancn/fuel-main-dev,zhaochao/fuel-main,AnselZhangGit/fuel-main,teselkin/fuel-main,zhaochao/fuel-main,ddepaoli3/fuel-main-dev,SergK/fuel-main,dancn/fuel-main-dev,ddepaoli3/fuel-main-dev,huntxu/fuel-main,stackforge/fuel-main,SmartInfrastructures/fuel-main-dev,stackforge/fuel-main,zhaochao/fuel-main,teselkin/fuel-main,teselkin/fuel-main,dancn/fuel-main-dev,huntxu/fuel-main,Fiware/ops.Fuel-main-dev,SmartInfrastructures/fuel-main-dev,SmartInfrastructures/fuel-main-dev,eayunstack/fuel-main,Fiware/ops.Fuel-main-dev,ddepaoli3/fuel-main-dev,stackforge/fuel-main,SergK/fuel-main,huntxu/fuel-main,zhaochao/fuel-main,eayunstack/fuel-main