To set domain-search for the system (that goes in /etc/resolv.conf), we currently do:

set system domain-search domain <domain1>
set system domain-search domain <domain2>
... etc.

This can be simplified to:

set system domain-search <domain1>
set system domain-search <domain2>
... etc.

This will shorten the path and also make consistent with domain-search config in other places (like dhcp-server).

Additionally, we can improve the smoketests for all resolvconf related configs.