Tighten check for HAE repos

Just an empty directory is not enough, there should be
repomd metadata in there. so check for the availability
of the metadata.
Merge pull request #352 from dirkmueller/master

Tighten check for HAE repos
Specify product and version for additional repositories (bnc#895086)

adapt the schema file

Add the new (not predefined) repositories from attributes
Merge pull request #349 from jsuchome/add_product_version_to_repos

Specify product and version for additional repositories (bnc#895086)