Use /bin/sh instead of /bin/bash

[mkhon]

Alpine Linux docker images do not have /bin/bash.
/bin/sh (which is usually a Korn Shell) is enough for pg_monz scripts.

[pengbo0328]

pg_monz needs /bin/bash environment and doesn't support /bin/sh.

[mkhon]

I believe I fixed all the places where bash'isms were used so the scripts can now be used as is on

• Alpine Linux
• Debian/Ubuntu minimal (without bash)
• *BSD (FreeBSD, NetBSD, OpenBSD)