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

Change-Id: I2b4e31aeab998ad4488a21a65cbcc5b3080900c5
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 11bdbd8..77da45f 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -28,6 +28,7 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux.git
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
 
 verifier:
   name: inspec