PgManager: Do not add NullHandler to logger. Rewrite get_instance(). ToolBase: fix prepare_conns() method.
### named connections
databases = {
'test' : 'host=127.0.0.1 user=test password=test dbname=test'
}
### meta database
# connection string (dsn) to meta db
meta_db = 'host=10.8.0.1 dbname=central'
# query from meta db, input is database name (will be placed instead of %s), output is values for create_conn
meta_query = '''SELECT host, port, dbname, user, password FROM config.databases WHERE name = %s LIMIT 1'''