Intensity setting for ipdevpoll jobs

When an ipdevpoll job starts polling 2000 devices simultaneously, this causes a tremendous load on a server. The devices need not be queried simultaineously for correct results, especially for the inventory job. In fact, when each single job instance extends in time, results may possibly be skewed.

The inventory job interval is 6 hours, ideally the work of this job could be spread out on these 6 hours to maintain a steady, low load, instead of giant load bursts. Each job specification in ipdevpoll.conf should have an integer setting called "intensity", which configures the maximum concurrently running instances of that particular job. When the maximum has been reached, further job instances will be delayed on startup. The default setting should be 0, meaning "no limit on the number of concurrent jobs".