For the HSM migration enhancement (LU-6081), it would be nice to be able to transfer data (stripe informaton and mdt_index) between lfs and the copytool in an exchange format, namely JSON.

The current liblustreapi_json.c can only encode JSON. Use the CCAN (Comprehensive C Archive Network) JSON which it relatively small, can encode/decode, and has a decent testsuite.

Replace liblustreapi_json.c with the new implementation.