Add a fake collector to produce loads of data
Adjust our drop heuristics to number of points

Based on analysis of our heaviest scollector host, the memory alloc
heuristic is not dependable. Almost everything worked correctly: we hit
100MB, points were dropped, when TSDB was back online the queue was
drained. Except that, after GC (verified because numgc was going up),
memory alloc wasn't decreasing. I assume this is due to implementation
detail in the OS or Go.

Instead, use 200k points (~140MB memory) as our metric. As further
protection against scollector gobbling all available memory, kill
ourself if we're above 500MB.