Breaking change to "runsc wait --checkpoint"

[Fabricio Voznika]

If you don't use runsc wait --checkpoint <num> you can stop reading now.

Commit fb730ff introduces a change that removes the <num> argument from the wait checkpoint call. This was done because, in most cases, the number is not known to the caller and there is no easy way to find out. This change makes the API simpler and easier to use.  To wait for a checkpoint now, just remove the number from the call:

runsc wait --checkpoint

Thanks,

Fabricio.