Remove CentOS upstream repos from rpm sandbox
Remove CentOS upstream repos from rpm sandbox

We need to remove CentOS upstream sandbox repos, which comes with
centos-release package before any yum operations.

Change-Id: I6322ab90c6aca744820446021432a78a2ba5f37a
Closes-bug: #1541871

stackforge/fuel-main,stackforge/fuel-main,SergK/fuel-main,SergK/fuel-main,SergK/fuel-main,stackforge/fuel-main