SST script for mariabackup (wsrep_sst_mariabackup.sh) does reverse DNS to convert
the joiner's IP address to domain name, and this is not always a wanted feature.

It is not understood why this remote host DNS conversion is in the script,
in the first place, but conversion was originally added by commit:

commit 3d8aacba
Author: Nirbhay Choubey <nirbhay.choubey@gmail.com>
Date:   Wed Feb 22 15:58:45 2017 -0500

In this commit, REMOTEHOST variable is removed and replaced by REMOTEIP. All
references to joiner is therefore by IP address only.