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

Change-Id: I0fe781390095fa078615d264477763cda2759efc
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 3afbc72..6d91fc5 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -18,6 +18,7 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux.git
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
   state_top:
     base:
       "*":