Ensured executor adapter propagates error and shutdown messages.
Ensured executor adapter propagates error and shutdown messages.

Prior to this patch, if an error, kill, or shutdown occurred during
subscription / registration with the agent, it was not propagated back
to the executor if the v0_v1 executor adapter was used. This happened
because the adapter did not call the `connected` callback until after
successful registration and hence the executor did not even try to
send the `SUBSCRIBE` call, without which the adapter did not send any
events to the executor.

A fix is to call the `connected` callback if an error occurred or
shutdown / kill event arrived before the executor had subscribed.

Review: https://reviews.apache.org/r/64070/

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