Apologies if I had a little more time, I would have had a go at submitting an actual change.

Whilst investingating some other problem, I accidentally uninstalled mariabackup without realising. My wsrep join began failing. however, it is failing without the intended error.

Having looked at how other wsrep providers handle this, I see there is a method in `wsrep_sst_common` called `wsrep_check_programs`. I wasn't sure of this was an oversight, or if there was a specific reason mariabackup is checked using an alternative mechanism.

BACKUP_BIN="$(command -v mariabackup)"

if [ ! -x "$BACKUP_BIN" ]; then

    wsrep_log_error 'mariabackup binary not found in path'

    exit 42

fi

+ pcmd='pv -f -i 10 -N joiner -F '\''%N => Rate:%r Avg:%a Elapsed:%t %e Bytes: %b %p'\'''

+ declare -a RC

++ command -v mariabackup

+ BACKUP_BIN=

UKQA DB-02:/etc/mysql/conf.d# echo $?

1

In contrast, this is what wsrep_sst_rsync uses

wsrep_check_programs rsync