LU-14707 tests: Prefer #!/bin/bash

LU-14707 tests: Prefer #!/bin/bash

Change remaining #!/bin/sh to use bash.
Add a warning to the git-hook about using
sh in shebangs. Using bash allows scripts to
freely use bash-isms and lowers the risks
of bugs on Debian based platforms.

Also, change remaining callers to use bash
rather than sh.

Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I10f3e8f71435c38cfc1650dd13168d7ed5d3b31f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49479
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: jsimmons <jsimmons@infradead.org>