Logging: don't disable existing loggers, avoid conflicting

An issue reported to upstream Ansible [1] highlighted that it was
fairly easy for the logging configurations of Ansible and ARA to
conflict with each other.

This commit makes it so we no longer set the root logger -- we don't
need to since we're not expecting orphaned loggers which would inherit
from the root configuration.

It also makes it so we don't disable existing loggers which would
prevent other software from being able to log properly.

And finally, it prefixes the names of the handlers and formatters
by "ara_" in order to prevent clashing with other software.

[1]: https://github.com/ansible/ansible/issues/41838

Change-Id: Iecc3324cc10a767b607d3055d6b93a12b9ae87ee

ara/config/logger.py

@@ -27,18 +27,19 @@ from ara.config.compat import ara_config
 DEFAULT_LOG_CONFIG = """
 ---
 version: 1
+disable_existing_loggers: false
 formatters:
-    normal:
+    ara_standard:
         format: '%(asctime)s %(levelname)s %(name)s: %(message)s'
 handlers:
-    console:
+    ara_console:
         class: logging.StreamHandler
-        formatter: normal
+        formatter: ara_standard
         level: INFO
         stream: ext://sys.stdout
-    file:
+    ara_file:
         class: logging.handlers.TimedRotatingFileHandler
-        formatter: normal
+        formatter: ara_standard
         level: {level}
         filename: '{dir}/{file}'
         when: 'midnight'
@@ -47,30 +48,26 @@ handlers:
 loggers:
     ara:
         handlers:
-            - file
+            - ara_file
         level: {level}
         propagate: 0
     alembic:
         handlers:
-            - console
-            - file
+            - ara_console
+            - ara_file
         level: WARN
         propagate: 0
     sqlalchemy.engine:
         handlers:
-            - file
+            - ara_file
         level: WARN
         propagate: 0
     werkzeug:
         handlers:
-            - console
-            - file
+            - ara_console
+            - ara_file
         level: INFO
         propagate: 0
-root:
-  handlers:
-    - file
-  level: {level}
 """
 
 
@@ -119,11 +116,14 @@ def setup_logging(config=None):
     ext = os.path.splitext(config['ARA_LOG_CONFIG'])[1]
     if ext in ('.yml', '.yaml', '.json'):
         # yaml.safe_load can load json as well as yaml
-        logging.config.dictConfig(yaml.safe_load(
-            open(config['ARA_LOG_CONFIG'], 'r')
-        ))
+        logging.config.dictConfig(
+            yaml.safe_load(open(config['ARA_LOG_CONFIG'], 'r'))
+        )
     else:
-        logging.config.fileConfig(config['ARA_LOG_CONFIG'])
+        logging.config.fileConfig(
+            config['ARA_LOG_CONFIG'],
+            disable_existing_loggers=False
+        )
 
     logger = logging.getLogger('ara.config.logging')
     msg = 'Logging: Level {level} from {config}, logging to {dir}/{file}'