Sync log module from oslo

This patch sync latest log module from oslo, bases on oslo-incubator
commit f06276bbdabd408549ecefa377b1349b57f5ac82.

DocImpact: Deprecate option log_config in favor of log_config_append.
Change option default_log_levels's default value.

Change-Id: Id2f7cf245499394554f6aa2c8d846cc9e2c2133a
Merge "Sync log module from oslo"