Unhardcode logger log level

This patch unhardcode log level in loggig.conf template.
The log level might be configured per logger by using the
following pillar structure:
 nova:
   controller:
     logging:
       loggers:
          <logger_name>:
            level: WARNING

Change-Id: Id7c5c73ee645f323028ba0acea27a2bc4026eb9c
Related-Prod: PROD-19782
2 files changed