CORD-382 update the sample config so the the example uses real values

Change-Id: Icef1ba9dbe726ceacaba1c2a8c20a1e4cd7763ec
(cherry picked from commit 9c18632fe70c732121f73a6fdeab4b2741bda4fe)
diff --git a/config/sample.yml b/config/sample.yml
index add8861..c594051 100644
--- a/config/sample.yml
+++ b/config/sample.yml
@@ -37,7 +37,7 @@
   #                     The value that this is compared against is the value return by
   #                     `ethtool -i <iface>` on the head and compute nodes.
   #
-  #fabric_iface_spec: one|two|three
+  #fabric_iface_spec: 'i40e|mlx4_en'
   fabric_ip: '10.6.1.1/24'
   management_ip: '10.6.0.1/24'
   external_ip: '47.135.132.21/24'