Define apache_name via a let block

Defining variables in rspec is dangerous since they end up being defined
on classes. That means that in a for loop it may end up being defined as
the last running version. A let block provides proper variable scoping.

This wasn't a problem until fb0d078
where it ran spec tests on all operating systems. Then it became
dependent on the order of the supported operating systems.

Fixes: fb0d078

Author: ekohl

spec/defines/vhost_spec.rb

@@ -5,14 +5,7 @@
 describe 'apache::vhost', type: :define do
   describe 'os-independent items' do
     on_supported_os.each do |os, facts|
-      apache_name = case facts[:os]['family']
-                    when 'RedHat'
-                      'httpd'
-                    when 'Debian'
-                      'apache2'
-                    else
-                      'apache2'
-                    end
+      let(:apache_name) { facts[:os]['family'] == 'RedHat' ? 'httpd' : 'apache2' }
 
       let :pre_condition do
         "class {'apache': default_vhost => false, default_mods => false, vhost_enable_dir => '/etc/#{apache_name}/sites-enabled'}"