Wrap socket_* calls with error-catching handlers

[asgrim]

At the moment in \Scoutapm\Connector\SocketConnector::sendCommand() for example, if there is a broken pipe, we get an error raised, for example:

[2019-12-16 13:30:58] local.ERROR: socket_send(): unable to write to socket [32]: Broken pipe {"exception":"[object] (ErrorException(code: 0): socket_send(): unable to write to socket [32]: Broken pipe at /home/james/workspace/scout-apm-laravel-blog/vendor/scoutapp/scout-apm-php/src/Connector/SocketConnector.php:103)
[stacktrace]
#0 [internal function]: Illuminate\\Foundation\\Bootstrap\\HandleExceptions->handleError(2, 'socket_send(): ...', '/home/james/wor...', 103, Array)
#1 /home/james/workspace/scout-apm-laravel-blog/vendor/scoutapp/scout-apm-php/src/Connector/SocketConnector.php(103): socket_send(Resource id #323, '\\x00\\x00\\x00e', 4, 0)
#2 /home/james/workspace/scout-apm-laravel-blog/vendor/scoutapp/scout-apm-php/src/Agent.php(320): Scoutapm\\Connector\\SocketConnector->sendCommand(Object(Scoutapm\\Events\\RegisterMessage))

Write a private function that adds an error handler to convert errors to exceptions (and use socket_last_error / socket_strerror to retrieve additional potentially useful error details) and bubble up to provide a more controlled error/exception flow.

The wrapped call to socket_connect in \Scoutapm\Connector\SocketConnector::connect can also be converted to use this new function.