Optimize ubuntu mirror build
Optimize ubuntu mirror build

Use apt-get `print-uris` option to fetch all the urls at once.
Then download them with xargs and wget in parallel.

Change-Id: I5825f4d3195c5869c3284a13ab68eacf406cf4be
Closes-bug: #1341566

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