wsrep_sst_mariabackup fails silently when mariabackup is not installed

The wsrep_sst_mariabackup SST script is executed with the bash '-e' option, so every execution of a command that returns a non-zero exit status will terminate the script, unless wrapped in a "set -e" / "set +e" block.

This is not used when trying to determine the absolute path to mariabackup, so when "which" fails here (which it does silently), the SST script will fail at this point, too:

INNOBACKUPEX_BIN=$(which mariabackup)

I propose to change the line above to:

set +e

INNOBACKUPEX_BIN=$(which mariabackup)

if test -z $INNOBACKUPEX_BIN

then

  wsrep_log_error 'mariabackup binary not found in $PATH'

  exit 42

fi

set -e