Improve the performance of Aggregate Graphs by Using VDEF's over Fetch and Assess to Calculate Nth Percentile and Bandwidth Usage

[TheWitness]

Feature Request

Is your feature request related to a problem? Please describe

Several years ago, RRDtool introduced VDEF's to make calculating totals of various dimension aggregations including ptiles and bandwidth summation. However, Cacti's implementation of nth percentile and bandwidth summation does not use them. This makes rendering Aggregate Graphs real slow especially when there are dozens of interfaces included.

Describe the solution you'd like

Convert the entirety of bandwidth summation and nth percentile to VDEF's to save CPU cycles and use RRDtool for calculating which will be much faster.