Give the same error message for wrong password and no such user
Give the same error message for wrong password and no such user

It's a bad idea to leak information about valid users, so we try not
to do that.  Fixes CHEF-822

ctdk/chef-server-webui,chef/chef-server-webui,chef/chef-server-webui,ctdk/chef-server-webui,ctdk/chef-server-webui