inputs.ping regression: Add back required "hostPinger" function for "exec" method

[sspaink]

Required for all PRs:

• Has appropriate unit tests.

fixes #8766

This pull request addresses the issue @NZSmartie found and reported in #8704. There was a regression due to the pr #8679 which removed a required function which led to a instant panic when using the "exec" method for inputs.ping. I added an integration unit test to cover for this case in the future that ensures init() is correct.

[telegraf-tiger]

🤝 ✅ CLA has been signed. Thank you!

[digitalcircuit]

Thank you for fixing this!

For those who have encountered this issue via an Internet search and want to downgrade Telegraf until a fixed release is available, as of now it is still possible to download the previous Telegraf version from the official downloads portal.

For example, on Debian/Ubuntu, instead of fetching telegraf_1.17.1-1_amd64.deb, you'd download telegraf_1.17.0-1_amd64.deb.

[srebhan]

Looks good to me.

@digitalcircuit can you confirm that this change fixes the problem?

[srebhan]

@sspaink please add a "Fixes #..." to the PR description. This way the issue is also closed when this is merged IIRC.

[digitalcircuit]

@srebhan Pardon the delay, I've only just now had the time to test this.

✔️ After compiling from source and building the appropriate package (had to also install fpm), Telegraf works with the same configuration that had previously crashed!

$ sudo dpkg -i telegraf_1.18.0~244178e5-0_amd64.deb
[…trimmed dpkg output…]
$ systemctl status telegraf.service
[…]
     Active: active (running) since Thu 2021-01-28 14:22:07 EST; 3min 18s ago
[…]
$ telegraf --version
Telegraf unknown (git: master 244178e5)

[tarjei]

Any ETA on when the PPAs will be updated?