Daemon client fails while closing connection to the daemon

[ghale]

When a build completes in the daemon, it sends the result back to the daemon client, along with a "build complete" message and then waits for a "finished" message from the client. Once the client receives the complete message, it then sends the "finished" message. The daemon waits for up to 60s to receive the finished message before giving up and closing the connection. There are a few scenarios where this could cause a problem:

• The client is delayed in sending the finished message (possibly because it is flooded with log messages, or some other spurious delay). The daemon can timeout and close the connection, causing a failure when the client tries to send the finished message.
• The daemon sends the complete message and then suffers a failure while waiting for the finished message. This could be because the daemon experiences an OOM or a daemon expiration event, but the end result is that the connection is closed before the finished message is sent. When the client tries to send the finished message, it gets a failure.

Expected Behavior

Since the build itself succeeds, we expect the build invocation to succeed, even if there are some communication failures while closing the connection to the daemon.

Current Behavior

When the client tries to send the "finished" message it gets a socket error, causing the build invocation to fail, even if the build itself succeeded.