Log settings not persistent

[shawnp0wers]

Describe the bug
When adjusting which events appear in the log (using lotus-miner log set-level --system xxx), the settings only persist until the miner is restarted. If they could be set in config, or persisted in some other way, it would be ideal.

To Reproduce
Change log setting. Restart miner. Log settings revert to default.

Expected behavior
Settings stick, or another method to set desired log levels.

Version (run lotus version):
Daemon: 1.2.2+git.b13226bc2.dirty+api1.0.0
Local: lotus version 1.2.2+git.b13226bc2.dirty

[Kubuxu]

I would like to avoid adding a persistent state to logging it can be problematic.
We could consider adding per-system log level via env-vars.

[f8-ptrk]

while on it: it would be great if we could not only set but query the levels of a system

[Stebalien]

See ipfs/go-log#100.