Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Update all script shebangs to use /usr/bin/env interpreter instead of /bin/interpreter

This is required to support systems where bash doesn't reside in /bin (such as NixOS, or the *BSD family) and allow users to specify a different interpreter version through $PATH manipulation.
https://www.cyberciti.biz/tips/finding-bash-perl-python-portably-using-env.html
```release-note
Use /usr/bin/env in all script shebangs to increase portability.
```