config file option for dir/file permissions

[pjaitken]

All elements created by chunkio.c:check_root_path and cio_stream.c:check_stream_path are created with hard-coded mode 0755. Therefore anyone can read the data; it is not confidential.

Provide a config file option allowing a user-configurable permission to be defined, eg 0700.

[edsiper]

/assigned to @leonardo-albertovich

we might add a function to setup those defaults