Evaluate radcli as potential freeradius-client replacement

@godfryd found a radcli project (github/webpage), which is a fork of FreeRADIUS client.

Its main advantage is that it's present in many OSes (e.g. libradcli-dev package on Ubuntu). This should make the code installation easier for users. Since the code is a fork of the original FreeRADIUS client, there's a chance it may not be that big deal to either support both or perhaps switch to radcli.

The goal of this ticket is to do an experiment and then:

• if easy to do, just do it
• if tricky to do, create appropriate ticket explaining what would have to be done
• if impossible or requires rewriting our code, just document here and close the ticket