Improve response logging

[cladelpino]

The relevant part of locallib.php which sets the string to be logged in the response_answer event is:

$status = 'Error sending request';
if (!empty($response['HTTP/1.1'])) {
$status = $response['HTTP/1.1'];
}

This leads, for instance, when response is 'HTTP/2' that the log gets written "Error sending request" and nothing else.

I'd suggest something like:

$status = json_encode($response);

to get more information logged, or at least also check for the HTTP/2 field of the response.