dockerd allows the `--log-level` to be specified, but this log-level
was not forwarded to the containerd process.
This patch sets containerd's log-level to the same as dockerd if a
custom level is provided.
Now that `--log-level` is also passed to containerd, the default "info"
is removed, so that containerd's default (or the level configured in containerd.toml)
is still used if no log-level is set.
Before this change:
containerd would always be started without a log-level set (only the level that's configured in `containerd.toml`);
```
root 1014 2.5 2.1 496484 43468 pts/0 Sl+ 12:23 0:00 dockerd
root 1023 1.2 1.1 681768 23832 ? Ssl 12:23 0:00 \_ docker-containerd --config /var/run/docker/containerd/containerd.toml
```
After this change:
when running `dockerd` without options (same as current);
```
root 1014 2.5 2.1 496484 43468 pts/0 Sl+ 12:23 0:00 dockerd
root 1023 1.2 1.1 681768 23832 ? Ssl 12:23 0:00 \_ docker-containerd --config /var/run/docker/containerd/containerd.toml
```
when running `dockerd --debug`:
```
root 600 0.8 2.1 512876 43180 pts/0 Sl+ 12:20 0:00 dockerd --debug
root 608 0.6 1.1 624428 23672 ? Ssl 12:20 0:00 \_ docker-containerd --config /var/run/docker/containerd/containerd.toml --log-level debug
```
when running `dockerd --log-level=panic`
```
root 747 0.6 2.1 496548 43996 pts/0 Sl+ 12:21 0:00 dockerd --log-level=panic
root 755 0.7 1.1 550696 24100 ? Ssl 12:21 0:00 \_ docker-containerd --config /var/run/docker/containerd/containerd.toml --log-level panic
```
combining `--debug` and `--log-level` (`--debug` takes precedence):
```
root 880 2.7 2.1 634692 43336 pts/0 Sl+ 12:23 0:00 dockerd --debug --log-level=panic
root 888 1.0 1.1 616232 23652 ? Ssl 12:23 0:00 \_ docker-containerd --config /var/run/docker/containerd/containerd.toml --log-level debug
```
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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