Need to insert a processing instruction into the generated file.

Fix bug 1068330

Change-Id: I7d61d4a9f0832e0bfd15bc6da7c7995195194404
Reviewed-on: https://review.openstack.org/19968
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins