Fix compatibility with Python 2.6 `LoggerAdapter`
Fix compatibility with Python 2.6 `LoggerAdapter`

The `logger` passed to our `DiskFile` by Swift uses a `LoggerAdapter`,
which has no `isEnabledFor` method in Python 2.6. This work-around calls
the method conditionally.

See: 8d3a0ca33aec6d2acad0c362074d557a9bf9b939

scality/ScalitySproxydSwift,scality/ScalitySproxydSwift