import from borel

See also https://github.com/anchor/borel/pull/92
Yeah, my bad here. There's been a lot of drift with how things were implemented.

A few things.

1) This should really be called deltaQuery, gauge is not processed like this at all.

Things like number of vcpus are gauges, and all of them are processed as consolidatedPollsters because the value in the SimplePoint does not necessarily represent the real value. For things like Memory Allocation they do, if at time x there is a point with value 2048, then at that time 2048MB was allocated, but things like instances are represented a hash.

2) This does not necessarily belong under Ceilometer. Gauge, Cumulative and Delta metrics are not bound to Ceilometer. (E.g. IPTraffic is a Delta metric (though currently as per (1) is called a Gauge metric) I'll clean this up with @tranma?