Yet another bug in the DNF module - really a troublesome one. Only call
the dnf updateinfo every interval, not every second. That significantly
reduces CPU load.
Due to name-clashing of the datetime module's "time" alias, time.sleep
didn't work (as it was looked up from the i3bumblebee module),
consequently, the DNF poll thread exited.
While at it, "beautify" the thread cancelling a bit by waiting until
the main thread is not running anymore.
Pass the "output" object to the modules' constructor to allow them to
define their own callbacks.
Any user-provided callbacks take precedence and override those of the
module.
Add a module that periodically (by default, once every 30min) calls
"dnf updateinfo" and evaluates the results to report the number of
bugfixes, enhancements, etc.
If there's either too many pending updates, or at least one security
update, the module goes critical.
