New client not gracefully closed on error if it has grabbed the pipe/socket

[saurabh21289]

I've seen this issue occur on Windows when the osquery process is terminated. The osquery-go end of the named pipe is not released and any attempts to re-establish communication begins to fail with error due to the pipe not being available. This behaviour continues unless we Shutdown() the extension manager. This will not be necessary if we call serverClient.Close() when error is encountered due to osquery process being killed.