[CentOS] CentOS Extras SRPMs for 7.1 / 7.2

Hello,

I noticed that recent source repositories for CentOS Extras packages do not have SRPMs for each available RPM.

In particular, I wanted to download the SRPM for cloud-init. After enabling the extras-source repository, `yumdownloader --source cloud-init` doesn't find any package.
This used to work on CentOS 7.0.

See the content of the following two repos:

	http://vault.centos.org/7.2.1511/extras/Source/SPackages/
	http://vault.centos.org/7.1.1503/extras/Source/SPackages/

compared with http://vault.centos.org/7.0.1406/extras/Source/SPackages/

It looks like only packages which were updated have made it in the newer repositories.

Thanks,
Pierre