Don't create files in /etc/iproute2 out of thin air

[Infinoid]

Fixes: #164

[Infinoid]

I was not able to run your unit tests; I get a timeout after 10 minutes. Please let me know if it breaks anything else.

I tested this using one of my own tests; it worked for me.

Before patch:

• no /etc/iproute2 directory
• run test (success)
• /etc/iproute2 exists
• /etc/iproute2/group file exists and is empty

After patch:

• no /etc/iproute2 directory
• run test (success)
• no /etc/iproute2 directory

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 50.64%. Comparing base (1f3a281) to head (7cd1773).

Files	Patch %	Lines
pkg/exec.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #165 +/- ## ========================================== + Coverage 50.48% 50.64% +0.15% ========================================== Files 67 67 Lines 3207 3197 -10 ========================================== Hits 1619 1619 + Misses 1362 1352 -10 Partials 226 226 ```

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