This commit changes the shebang in all shell scripts from absolute
paths (such as `/bin/bash` or `/usr/bin/python3`) to the `/usr/bin/env`
binary with the accompanying interpreter as it's argument.
The reason for this are as follows:
- NixOS cannot work with absolute paths
- BSD systems install their packages in /usr/local/bin
It turns out that the clone-and-hack in tests/chutney/arti-bench
was not identical to the original in tests/chutney/setup.
I diffed the two and preferred the version from arti-bench.
Formerly, the "launch a chutney network" code was duplicated in
"setup" and "arti-bench", since "setup" always launched an arti
proxy, while "arti-bench" didn't want that functionality.
Now the "setup" script launches an arti proxy conditionally,
depending on whether the "proxy" argument is given.
As per #309
Update all references. There is one remaining hit for
git-grep '\.sh\b'
namely "build.sh" in maint/reproducible_build, which I think is
the build script for osxcross - ie, an external project.