galera_new_cluster is not POSIX-compliant

The standard shell in Ubuntu is dash, but the bootstrap command galera_new_cluster is not POSIX-compliant. galera_new_cluster's shebang looks like:

#!/bin/sh

which is a link to dash on ubuntu:

root@galera-training-0:~# ls -ln /bin/sh

lrwxrwxrwx 1 0 0 4 Feb 16 08:37 /bin/sh -> dash

this results in this error:

root@galera-node-0:~# galera_new_cluster

/usr/bin/galera_new_cluster: 8: [: unexpected operator