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

Change-Id: I1b8420decb590285ad817be46212fa224afa531e
Related: PROD-29251
diff --git a/.kitchen.yml b/.kitchen.yml
index 23a5cd1..2a2c227 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -37,6 +37,7 @@
     - name: linux
       repo: git
       source: https://gerrit.mcp.mirantis.com/salt-formulas/linux.git
+      branch: <%=ENV['GERRIT_BRANCH'] || 'master' %>
 
 verifier:
   name: inspec