To support handling OOM situation when incoming slot migration is executing variable is_oom_ was introduced in ConnectionContext as a way to signalizing back OUT_OF_MEMORY command status (PR #5000).

This was comprise not to be too much intrusive in existing code but still have functionality that was need to develop this feature.

Unfortunately, this variable conceptually is more tied to the command rather than the connection context.

1. At least remove this variable from ConnectionContext and put it where it is more appropriate.
2. Make command status to be available after DispatchCommand as a more generic way to handle this and future implementation that depends on command status.