Wait when encountering update in progress

[bittrance]

Today, when cuffsert encounters an update in progress, it aborts. It would be useful if it waited for the previous process to complete before starting the new operation. When waiting for the previous run to complete, we should output stack events as they occur. At this point it must ask confirmation regardless of severity of change (still respecting --dry-run and --yes).

It should also be possible to use this feature to "re-connect" in case cuffsert died for some reason. Ideally, if we detect no changes after the previous run was finished, we should just terminate and not echo the stupid "no changes" error, as if this was a single cuffsert run.

As a special case, it might be useful to be able to do --replace to abort the current operation by requesting to delete the stack (it seems to be possible to delete a stack even if it is in progress) and then creating it anew.