Do not use jsonevent-layout for error logs in JSON format
So far the net.logstash.log4j.jsonevent-layout package was used to
format the error logs to JSON. This format was not suitable for the
httpd- and sshd logs and thus was not used there. Also the format
provided by the dependency was not configurable, e.g. did not allow
to change the timestamp. This resulted in different timestamp formats
for the text- and the json-formatted error logs.
To be more flexible in the formatting of the json logs, this change
removes the dependency. It keeps however the ISO8601-formatted timestamp,
but adds the timezone offset and thus does not assume the UTC timezone.
In a followup change the timestamps of all logs will be adapted to the