Add step to Debian 9 to fix permissions on /mnt/librenms/rrd/journal/
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I tried to get these to as few of steps as possible.
Ubuntu starts the service during installation, so it won't have proper permissions/settings until after you restart it.
CentOS doesn't need epel (it doesn't have rrdtool in it) or permissions fixes. Move run files to /run directory to save a lot of steps and be similar to other platforms. Skipping the touch allows us to skip daemon-reload
* Fix the Ubuntu 16 rrdcached config
Missing user and group to run as and the -R option
* Create RRDCached.md
Add write threads in case users need to tune performance (4 is the default)
