mirror/centos: fix downloading of src.rpm's
mirror/centos: fix downloading of src.rpm's

An old version was downloading everything (including the upsteam sources)
and completely ingnoring errors. As a side effect only used to be
downloaded. Later on a proper error handling has been added, which break
downloadin src.rpm's. Fix the download rules so only Mirantis' sources
get fetched.

Change-Id: I1c43e0bb38a7fea34f1c7b2b9eb701a734341268
Closes-Bug: #1418390

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