Specify logging in new XML format

[mstormi]

Once more I had logging fill the (SD) disk and came to think if we should limit that better in openHABian.
(EDIT: or change OH's default ?)

We should limit the size and number of logs, and unlike OH default config, we should gzip them.
Attention: we must NOT use any external tool such as logrotate for OH logs! log4j2 handles this.

Unfortunately, the config format to spec what's logged and how it's treated - specified in /var/lib/openhab/etc/log4j2.xml - has changed to xml and all the information I have (for now) is in the old format.
http://karaf.apache.org/manual/latest/#_log4j_v2_support
openhab/openhab-docs#1163

For reference, stuff to change in old format:

log4j2.appender.event.strategy.type = DefaultRolloverStrategy
log4j2.appender.event.strategy.max = 7

log4j2.appender.event.strategy.fileIndex = min
(not sure if that last is required)

log4j2.appender.out.filePattern = ${openhab.logdir}/openhab.log.%i.gz
(to have it gzip logfiles)

[ecdye]

I don't see any problem with this. It may even help solve a problem which is kind of nice too.

[mstormi]

Fixed-By: openhab/openhab-distro#1312