Rename csv_utils to _csv_utils and fix imports

[Ulincsys]

Description

• Rename csv_utils.py to _csv_utils.py
  • Any PY file in the augur/application/cli directory is assumed by Click to be a CLI multicommand submodule, unless that file's name begins with an underscore _. The csv_utils.py file is not a multicommand submodule, and so must be prefixed with an underscore to exclude it from dynamic loading during multicommand processing.
• Fix util imports
  • The augur.application.cli.tasks multicommand submodule previously imported clear_rabbitmq_messages and raise_open_file_limit from the base backend multicommand submodule, but they have since moved to augur.application.cli._cli_util

With this patch, running augur --help successfully loads all multicommand submodules and displays the global help message.

This PR fixes #3627

Signed commits

• Yes, I signed my commits.

[shlokgilda]

LGTM

[MoralCode]

I dont like the idea of renaming a shared utility like this because of a unique issue with click. I didnt see another way until i read:

but they have since moved to augur.application.cli._cli_util

This makes me think: could we import the needed csv utils in this already-prefixed CLI util file instead and then wherever its needed in the CLI can import it from that already-prefixed file?

[Ulincsys]

I dont like the idea of renaming a shared utility like this because of a unique issue with click.

Is there a specific objection you have as to why renaming the file is improper?

It doesn't really matter to me how this issue gets resolved, I just took the approach that required the least changes to achieve the desired effect.

[MoralCode]

Is there a specific objection you have as to why renaming the file is improper?

A bad assumption that this utils file existed somewhere else in the code and that we were having the CSV module dictate filenames outside of its module.

I think this is fine for now. Long term I think id like to find a better way to discover click modules (maybe an AST parsing based system to lightly parse each file?), but this is fine for now