Fix 8.0 custom iso/upgrade jobs

[Vladimir Kozhukalov]

For example http://jenkins-product.srt.mirantis.net:8080/view/custom_iso/job/custom_8.0_iso/67/consoleFull

The reason why those packages could not be downloaded is that simlink was updated while iso was being built.

[Fuel Devops McRobotson (fuel-devops-robot)]

Related fix proposed to branch: master
Change author: Sergey Kulanov <email address hidden>
Review: https://review.fuel-infra.org/12056

[Fuel Devops McRobotson (fuel-devops-robot)]

Reviewed: https://review.fuel-infra.org/12056
Submitter: Aleksandra Fedorova <email address hidden>
Branch: master

Commit: 0ea4bdec180d6584e1d8815118bff671ac203d2f
Author: Sergey Kulanov <email address hidden>
Date: Wed Sep 23 19:30:09 2015

[custom_iso] Use perestroika mirrors from the latest snapshots

We have to use the latest snapshot mirrors (both Ubuntu, Centos) from
perestroika. Since we have perestroika mirrors in all locations we can
try to select the closest one

Change-Id: I8c844b7f151ae0abd687902d134f532e472b7ca0
Related-bug: #1498931