chore: refactor error log for manager api

[nic-chen]

relate to #620

• Currently only panic logs are retained, errors are just respond by apis. we need to retain error logs.
• Support custom error log level
• Support saving to a local file, and can customize the file path
• Support log rotate

we could use zap that most gophers recommend.

[membphis]

https://github.com/cilium/cilium/blob/master/pkg/logging/logging.go

it seems a good choice.

[nic-chen]

@membphis
it use github.com/sirupsen/logrus

zap is better than logrus for us, I'm sure about that.

[membphis]

nice @nic-chen ^_^

can you list some reason? We need to why.

[nic-chen]

nice @nic-chen ^_^

can you list some reason? We need to why.

it has almost the same feature and much faster. and it support atomic level, sampling .. etc advanced features

[membphis]

Nice got it. And I check the license, it is MIT, good for us too.

Please confirm whether it will introduce new dependent libraries and their licenses are acceptable.

[nic-chen]

done.

rotate should be done with access log feature or after that.