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
diff --git a/README.rst b/README.rst
index 3cf25d0..bf4cbe2 100644
--- a/README.rst
+++ b/README.rst
@@ -753,6 +753,25 @@
             ossyslog:
               enabled: true
 
+The log level might be configured per logger by using the
+following pillar structure:
+
+.. code-block:: yaml
+
+  nova:
+    compute:
+      logging:
+        loggers:
+          <logger_name>:
+            level: WARNING
+
+  nova:
+    compute:
+      logging:
+        loggers:
+          <logger_name>:
+            level: WARNING
+
 Inject password to VM
 ---------------------