support change the level of etcd for debugging

[csuzhangxc]

Feature Request

Is your feature request related to a problem? Please describe:

If etcd started failed, we may not know the reason because we only logging error level log.

Describe the feature you'd like:

support to change the level of etcd log with/without adding any new config items (or output the log to other files).

NOTE: always using `info` level often has too many logs.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: