added pinning for mcp repos, mk-apt and contrail

Change-Id: I3ca753e11290df0cf0727b3d8cbb18b2324c6f86
diff --git a/linux/system/repo/mcp/extra.yml b/linux/system/repo/mcp/extra.yml
index d8977f4..49e4532 100644
--- a/linux/system/repo/mcp/extra.yml
+++ b/linux/system/repo/mcp/extra.yml
@@ -9,3 +9,7 @@
           architectures: amd64
           key_url: "http://apt-mk.mirantis.com/public.gpg"
           clean_file: true
+          pin:
+          - pin: 'release a=${_param:openstack_version}-holdback'
+            priority: 1100
+            package: '*'