Rebuilding Poller Cache from Utilities does not respect poller interval due to lack or ordering

[TheWitness]

Describe the bug

If you have a poller interval of say 5 minutes and a cron interval of 1 minute, data sources should be spread out amongst hosts. When you rebuild the poller cache, this distribution should be updated, and presently it's not.

To Reproduce

Steps to reproduce the behavior:

1. Setup a system as defined above

2. Create a number of hosts and graphs

3. See look into the poller_item table, there should be 5 distinct groupings of rrd_next_step

4. Goto utilities and Repopulate the Poller Cache

5. Not now that that fairly equal distribution of rrd_next_steps is now broken

Expected behavior

Cacti should evenly distribute poller items between various intervals.

Specific Queries

 select rrd_next_step, count(*) as items from poller_item group by rrd_next_step;
+---------------+-------+
| rrd_next_step | items |
+---------------+-------+
|             0 |   244 |
|            60 |   243 |
|           120 |   244 |
|           180 |   246 |
|           240 |   180 |
+---------------+-------+
5 rows in set (0.001 sec)