INT-2911 IO Exceptions Not Logged as ERROR

TcpNetConnection IO errors were only logged under DEBUG.

* Code was added to suppress the error log when the exception was due to a normal close. This inadvertently suppressed all ERROR logs.
* Capture a local copy of this.noReadErrorOnClose before closing the socket after an exception.
* Add test case to ensure ERROR log is emitted.
Merge pull request #728 from garyrussell/INT-2911

* garyrussell-INT-2911:
  INT-2911 IO Exceptions Not Logged as ERROR