Fix the case statement

If do not set the case will lead to this lint warning of
"case statement without a default case"

Change-Id: I4ae65791e7a89c9407e14708db32a53790b72f9e

spec/acceptance/basic_panko_spec.rb

@@ -40,6 +40,9 @@ describe 'basic panko' do
             ssl => false,
           }
         }
+        default: {
+          fail("Unsupported osfamily (${::osfamily})")
+        }
       }
       EOS