crushtool: new cli tests for the vary-r tunable

These illustrate the variation in mapping results as the vary_r tunable
is adjusted.  In particular, for a legacy cluster, we can use a value like
4 to minimize the number of PGs that move while now getting the valid
mappings that we need.

The crushmap here comes from a customer who was seeing a bad mapping for
certain pgs after some OSDs were reweighted by utilization.

Signed-off-by: Sage Weil <sage@inktank.com>
crush: add firefly tunables baseline test

This is a user's map that gives different results when the vary_r tunable
is adjusted.

Signed-off-by: Sage Weil <sage@inktank.com>