Add salt-formulas repo

  * Correct pinning
  * At mirror.mirantis.com
  * Unclude update|hotfix stubs

Prod-related: PROD-25034 (PROD:25034)

Change-Id: I3d776ac1d9b15187ae9920be476f14cfcccec969
diff --git a/linux/system/repo/mcp/salt/init.yml b/linux/system/repo/mcp/salt/init.yml
index 3430a5c..b3609bb 100644
--- a/linux/system/repo/mcp/salt/init.yml
+++ b/linux/system/repo/mcp/salt/init.yml
@@ -1,3 +1,4 @@
+# DEPRECATED since 2018.12+ release.
 parameters:
   _param:
     linux_system_repo_mcp_salt_version: ${_param:mcp_version}