Run the munin-stats plugin as the munin user so it can read the logs

Otherwise it runs as user nobody, group munin and can't read the files:

    root@bm-n2:~# munin-run --debug munin_stats
    # Processing plugin configuration from
    # /etc/munin/plugin-conf.d/munin-node
    # Set /rgid/ruid/egid/euid/ to /110/65534/110 110 /65534/
    # Setting up environment
    # About to run '/etc/munin/plugins/munin_stats'
    update.extinfo Can't open /var/log/munin/munin-update.log for reading
    update.value U
    graph.extinfo Can't open /var/log/munin/munin-graph.log for reading
    graph.value U
    html.extinfo Can't open /var/log/munin/munin-html.log for reading
    html.value U
    limits.extinfo Can't open /var/log/munin/munin-limits.log for reading
    limits.value U

    root@bm-n2:~# ls -l /var/log/munin/munin-{update,graph,html,limits}.log
    -rw-r----- 1 munin adm 1279972 Feb  2 02:40 /var/log/munin/munin-graph.log
    -rw-r----- 1 munin adm   64711 Feb  2 02:40 /var/log/munin/munin-html.log
    -rw-r----- 1 munin adm   87572 Feb  2 02:40 /var/log/munin/munin-limits.log
    -rw-r----- 1 munin adm  282695 Feb  2 02:40 /var/log/munin/munin-update.log
The exim munin plugins are named exim_* not exim4_*; run them using Debian-exim

If this was working in the past then the munin exim plugins changed
names and dropped the 4.  I don't see that the exim munin plugins
themselves are provisioned from puppet, so who knows where they came
from.
Merge pull request #22 from CPAN-API/munin-permissions

Munin permissions