Make sure kitchen test dependencies formulas are always fetched from correct branch

Change-Id: I09c428a408a15f1adbc1d6327241a8b358fbe066
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 6b272e7..1826970 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -27,6 +27,7 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
 
 verifier:
   name: inspec