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/ubuntu-16.04/scripts/salt.sh b/ubuntu-16.04/scripts/salt.sh
index eba5bca..b1a1389 100644
--- a/ubuntu-16.04/scripts/salt.sh
+++ b/ubuntu-16.04/scripts/salt.sh
@@ -4,10 +4,19 @@
 SALTSTACK_GPG=${SALTSTACK_GPG:-"https://mirror.mirantis.com/proposed/saltstack-2017.7/xenial/SALTSTACK-GPG-KEY.pub"}
 
 wget -O - ${SALTSTACK_GPG} | sudo apt-key add -
-echo "${SALTSTACK_REPO}" > /etc/apt/sources.list.d/saltstack.list
+echo "${SALTSTACK_REPO}" > /etc/apt/sources.list.d/mcp_saltstack.list
 
-# We expect issues with GPG,related to our mirrors - so temporary disable check.
-echo "APT::Get::AllowUnauthenticated true;" > /etc/apt/apt.conf.d/99allow_unauthenticated
+# This Pin-Priority fil should be always aligned with
+# https://github.com/Mirantis/reclass-system-salt-model/blob/master/linux/system/repo/mcp/apt_mirantis/saltstack.yml
+cat <<EOF >> /etc/apt/preferences.d/mcp_saltstack
+Package: libsodium18
+Pin: release o=SaltStack
+Pin-Priority: 50
+
+Package: *
+Pin: release o=SaltStack
+Pin-Priority: 1100
+EOF
 
 apt-get update
 apt-get -y install salt-minion
@@ -25,4 +34,5 @@
 EOF
 
 rm -vf /etc/apt/apt.conf.d/99allow_unauthenticated
-rm -vf /etc/apt/sources.list.d/saltstack.list
+rm -vf /etc/apt/sources.list.d/mcp_saltstack.list
+rm -vf /etc/apt/preferences.d/mcp_saltstack