MINOR: cli/threads: always bind CLI to thread group 1

MINOR: cli/threads: always bind CLI to thread group 1

When using multiple groups, the stats socket starts to emit errors and
it's not natural to have to touch the global section just to specify
"thread 1/all". Let's pre-attach these sockets to thread group 1. This
will cause errors when trying to change the group but this really is not
a problem for now as thread groups are not enabled by default. This will
make sure configs remain portable and may possibly be relaxed later.