Fix alembic 'No handlers could be found for logger...'

When running 'neutron-db-manage upgrade heads', I get:

No handlers could be found for logger "oslo_config.cfg" <--
INFO  [alembic.runtime.migration] Context impl MySQLImpl.
...

This patch moves the logging configuration from env.py to cli.py,
so the configuration is done when the CLI is invoked and not
when Alembic imports env.py.

Change-Id: I767e72f513699f21dd629241faa04cb2d8fa416c

neutron/db/migration/alembic_migrations/env.py

@@ -12,8 +12,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from logging import config as logging_config
-
 from alembic import context
 from oslo_config import cfg
 import sqlalchemy as sa
@@ -40,10 +38,6 @@ MYSQL_ENGINE = None
 config = context.config
 neutron_config = config.neutron_config
 
-# Interpret the config file for Python logging.
-# This line sets up loggers basically.
-logging_config.fileConfig(config.config_file_name)
-
 # set the target for 'autogenerate' support
 target_metadata = model_base.BASEV2.metadata
 

neutron/db/migration/cli.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 import copy
+from logging import config as logging_config
 import os
 
 from alembic import command as alembic_command
@@ -62,6 +63,11 @@ BRANCHLESS_WARNING = 'Branchless migration chains are deprecated as of Mitaka.'
 
 neutron_alembic_ini = os.path.join(os.path.dirname(__file__), 'alembic.ini')
 
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+logging_config.fileConfig(neutron_alembic_ini)
+
+
 VALID_SERVICES = ['fwaas', 'lbaas', 'vpnaas']
 INSTALLED_SERVICES = [service_ for service_ in VALID_SERVICES
                       if 'neutron-%s' % service_ in migration_entrypoints]