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

Change-Id: Ia36fb24d3a1959b025582225745b1c6aa60a3e29
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 9256945..476c50a 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -28,6 +28,7 @@
     - name: linux
       repo: git
       source: "https://gerrit.mcp.mirantis.com/salt-formulas/linux"
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
 
 verifier:
   name: inspec