Fix libsodium downgrade issue

  * For some reason, apt going to be crazy
    if found identical pkgs in different repos:

apt-cache policy libsodium18
libsodium18:
  Installed: 1.0.8-5
  Candidate: 1.0.8-5
  Version table:
 *** 1.0.8-5 500
        500 http://mirror.mirantis.com/proposed/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status
     1.0.8-5 500
        500 https://mirror.mirantis.com/testing/saltstack-2017.7/xenial xenial/main amd64 Packages
   So, lets pin it from the began to _one_ repo
   * Misc: switch to always use staric bootstrap.saltstack.com.sh
           remove non-relevant anymore AllowUnauthenticated

Closes-Bug: PROD-22326 (PROD:22326)

Change-Id: Ib9f7cdd1bcfb1451b1e17dfcdacadace249cccc3
diff --git a/common/ubuntu_cleanup.sh b/common/ubuntu_cleanup.sh
index c469bbd..3097bee 100644
--- a/common/ubuntu_cleanup.sh
+++ b/common/ubuntu_cleanup.sh
@@ -5,6 +5,7 @@
 
 rm -rf /var/lib/apt/lists/*
 rm -rv /etc/apt/sources.list.d/* || true
+rm -rv /etc/apt/preferences.d/* || true
 echo > /etc/apt/sources.list  || true
 rm -vf /usr/sbin/policy-rc.d || true