We need a better mechanism to handle `sys.exit()` in library code

[npalaska]

Currently there are lot of instances in lib/pbench/cli/agent/commands/results/__init__.py where we use sys.exit() which leads to some undesirable behaviors.

We should never use sys.exit() library code.

See the comment #1947

[riya-17]

@portante Isn't this issue been resolved with #2189 PR? Or is there some more work that needs to be done?

[portante]

More work; I'd start by reviewing all the code in the library that calls sys.exit().