Previously, multiple parallel writes extending file size through NFS were
racing with each other and triggering deletions of part of the written data
I.e. if you mounted vitastor-nfs and just copied a file into it in MC then
you could end up with only a part of the file actually written
Return results and errors in a variable instead of just printing them,
separate vitastor-cli main() from cli_tool_t, move positional argument
parsing to CLI main from command implementations.