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

Change-Id: Iba65f407a760b018e40499aba83c051fdd89135a
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 10686ea..e4a7b06 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -18,6 +18,7 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
   state_top:
     base:
       "*":