Mirror GPG keys

Hello, I'm using upstream_sync.py to mirror the OpenHPC repository, but the script is missing the GPG key files.

In example: http://build.openhpc.community/OpenHPC:/1.3/updates/CentOS_7/repodata

The key file is located on `repomd.xml.key` file.

So the point is: there's a way to mirror this file with upstream_sync.py? Is this supported?
