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

Change-Id: I6e713b0e1b257c718e5e714ae4674e945c717936
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 24c1942..69913c6 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:
       "*":