Add option --refreshrepo

[tdgroot]

With this, one can tell dnf to refresh specific repos, like so:

dnf upgrade --refreshrepo='fedora,remi'

Please let me know what can be improved!

By the way, I'm making use of the _SplitCallback, which splits on , or whitespace. I'd like to just split on the , character. Is there an existing callback I can reuse for that?

[tdgroot]

The integration test fails because it's got the options list baked in:

[kontura]

First of all sorry for our non responsiveness I suspect the reason for it is that none of us really know what to do about your changes. Now that we had an internal discussion about it we decided against merging this. The new option has a very specific use case and it would perhaps be better suited for a plugin or possibly even an alias. You can achieve the same effect by this workaround: dnf upgrade --setopt=fedora.metadata_expire=0 --setopt=remi.metadata_expire=0.