Add contentdir yum variable

The centos-release-qemu-ev repo package now supports $contentdir but
CentOS base has not fully caught up yet.[0]

[0] https://lists.centos.org/pipermail/centos-devel/2018-March/016542.html

Change-Id: I9e530b89092e0d4abb14750d4c181a7712c94e8c

recipes/default.rb

@@ -110,6 +110,16 @@ when 'rhel'
     action deps_action
   end
 
+  # TODO(sc): workaround to add $contentdir
+  #           removable when centos is updated
+  bash 'yum_contentdir' do
+    cwd ::File.dirname('/etc/yum/vars')
+    code <<-EOH
+      echo 'centos' > /etc/yum/vars/contentdir
+      EOH
+    not_if { ::File.exist?('/etc/yum/vars/contentdir') }
+  end
+
   package 'centos-release-qemu-ev' do
     action :upgrade
   end