When using curl multi, we populate the multi with handles and then
call multi_perform which leads to curl establishing the multi
connection and sending tranfers once it is done. This looks
satfisfying enough if we don't look at the time values stored by curl
in each handles. In this case it appears that all the transfer time
are set to the time the curl multi was started meaning that all
transfers keep track of the connection time, this is normal for the
first transfer but unnecessary for all the following ones.

Therefore by sending a first transfer asking for the root NS, it
allows to open the connection without populating the resolver cache.
And thus keeps the curl timers more accurate.