master: add start and stop log for munin-graph

As Christoph Biedl suggested, we should at least log the start and stop of the
cron part for munin-graph if enabled. That part was remove in 2.0.12, as commit
4372cdf24935b45f62a93b8f55e6ccacc4b6a687.

Closes: #1296
master: remove CGI reference in comments

As Christoph Biedl suggested, we should remove the CGI reference in the
munin-graph comments, as it's cron only anyway.

I agree, as wrong comment is much worse than no comment at all.
Merge branch 'fix-graph-log' into devel