Retrieve the FQDNs of systems in the susemanager API

[chiaradiamarcelo]

We need a way to obtain the FQDN of the peripheral servers.

At the moment we have a temporary solution, calling the "system.listFqdns" method in the susemanager API.
This present 2 problems:

• it's basically an N + 1 query problem
• The "system.listFqdns" can return more than one FQDN per system (at the moment we are keeping just the 1st one in such cases)

We should address both problems.