Nit: fix spec description

Fixes #544

Author: aramprice

bosh-stemcell/spec/stemcells/cloudstack_spec.rb

@@ -7,7 +7,7 @@
     end
   end
 
-  context "installed by bosh_disable_password_authentication" do
+  context "installed by base_ssh" do
     describe "disallows password authentication" do
       subject { file("/etc/ssh/sshd_config") }