nginx: switch to timestamps generated by syslog-ng

Since nginx only uses 1 second precision for the error logs and syslog
timestamps, we can use receive time on the syslog-ng side. We can switch
to source time once nginx adds RFC 5424 support which is currently in an
open pull request but will likely require changes to add a configuration
option for it. Our approach to working around this within nginx didn't
work perfectly since $msec obtains the time on-demand separately from
$time_iso8601.

Author: thestinger

nginx/nginx.conf

@@ -79,11 +79,7 @@ http {
     ssl_session_timeout 1d;
     ssl_buffer_size 4k;
 
-    map $time_iso8601&$msec $time_log {
-        ~(.+)\+.+&\d+\.(\d+) "$1.$2Z";
-    }
-
-    log_format main '$time_log $connection-$connection_requests $remote_addr $remote_user $ssl_session_reused $ssl_protocol $server_protocol '
+    log_format main '$connection-$connection_requests $remote_addr $remote_user $ssl_session_reused $ssl_protocol $server_protocol '
         '$host $request_method "$request_uri" $status $request_length $body_bytes_sent/$bytes_sent '
         '$request_time $upstream_connect_time/$upstream_header_time/$upstream_response_time '
         '$upstream_cache_status "$http_referer" "$http_user_agent"';