Paranoid bug fix.

If we replace our proxy service, then stop observing the prior instance.

This doesn't happen in practice, since we don't replace.
Race fix: don't post a task from a ref-counted constructor.

The posted task will increment the ref count, and in the worst case,
decrement it prior to your smart pointer incrementing the ref count.

This change introduces an explicit Start() method to the Cnet pool.
Ignore unittest log.