rpc: Convert last two calls to generated code

These two calls, “upload_file” and “write_ssconf_files” are treated
separated as they're used by the configuration, where we can't use the
normal resolver.

There's still some duplicated code in rpc.py, but that will be taken
care of in future patches.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>