node: retrieve logs from journal socket

[pires]

... instead of doing it through journalctl CLI.

This is the first step to address #5. What's missing and will eventually be addressed in separate PRs?

• follow mode support
• retrieving logs pertaining to the current Pod, in case a homonym Pod once existed for which journald still has entries for.

Some examples of a Pod named hello, that simply prints date, every 5 seconds:

kubectl logs --since:

$ k logs --since 20s hello
Thu Jan 21 23:20:52 WET 2021
Thu Jan 21 23:20:57 WET 2021
Thu Jan 21 23:21:02 WET 2021
Thu Jan 21 23:21:07 WET 2021

$k logs --since 1m hello
Thu Jan 21 23:20:17 WET 2021
Thu Jan 21 23:20:22 WET 2021
Thu Jan 21 23:20:27 WET 2021
Thu Jan 21 23:20:32 WET 2021
Thu Jan 21 23:20:37 WET 2021
Thu Jan 21 23:20:42 WET 2021
Thu Jan 21 23:20:47 WET 2021
Thu Jan 21 23:20:52 WET 2021
Thu Jan 21 23:20:57 WET 2021
Thu Jan 21 23:21:02 WET 2021
Thu Jan 21 23:21:07 WET 2021
Thu Jan 21 23:21:12 WET 2021

kubectl logs --timestamps - by default, kubectl has timestamps disabled:

$ k logs --since 20s --timestamps hello
2021-01-21 23:21:02.231042 +0000 WET Thu Jan 21 23:21:02 WET 2021
2021-01-21 23:21:07.23385 +0000 WET Thu Jan 21 23:21:07 WET 2021
2021-01-21 23:21:12.236292 +0000 WET Thu Jan 21 23:21:12 WET 2021
2021-01-21 23:21:17.238822 +0000 WET Thu Jan 21 23:21:17 WET 2021

kubectl logs --tail:

k logs --tail 10 hello
Thu Jan 21 23:22:07 WET 2021
Thu Jan 21 23:22:12 WET 2021
Thu Jan 21 23:22:17 WET 2021
Thu Jan 21 23:22:22 WET 2021
Thu Jan 21 23:22:27 WET 2021
Thu Jan 21 23:22:32 WET 2021
Thu Jan 21 23:22:37 WET 2021
Fri Jan 22 09:07:06 WET 2021
Fri Jan 22 09:07:11 WET 2021
Fri Jan 22 09:07:16 WET 2021

$ k logs --tail 2 hello
Fri Jan 22 09:07:21 WET 2021
Fri Jan 22 09:07:26 WET 2021