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

Change-Id: I0ff0f65bab2305c355b9c1cfb5073d810513f932
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index bd6c8fe..9e30b1d 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -31,6 +31,7 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux.git
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
 
 verifier:
   name: inspec