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

Change-Id: Idc8ed15f56c01252dddc74637e2ff33a3012049b
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index a808192..2616f4a 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -14,9 +14,11 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
     - name: nginx
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/nginx
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
   log_level: error
   formula: git
   grains: