Replace file.flush() calls with flush_sync() helper
    
    Calls to `os.fsync(f.fileno())` need to be accompained by `f.flush()`.
    
    Commit 8bbeedc93fd442cbbb9bb70e5f446011e95211db introduces the helper
    `ipapython.ipautil.flush_sync()`, which handles all calls in the right
    order.
    
    However, `flush_sync()` takes as parameter a file object with fileno
    and name, where name must be a path to the file, this isn't possible
    in some cases where file descriptors are used.
    
    Issue: https://pagure.io/freeipa/issue/7251
    
    Signed-off-by: Armando Neto <abiagion@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>