sort scan results by rack, board, and device

[edaniszewski]

We never really had true/complete sorting of scan results -- it used to just be sorted by rack id. Prior to that, it didn't have any sorting, but there was more consistency just based on configuration order.

This PR enforces sorting at the rack, board, and device level for scan results. As we start having more devices, this makes the scan much more consistent and easier to read through as a human.

related:

• Ensure fan_sensors order correctness. #188
• fan_sensors route. Sensors come in in random order. #116
• Lost sorting on scan results. #114

[codecov]

Codecov Report

Merging #193 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
+ Coverage   81.39%   81.43%   +0.04%     
==========================================
  Files          44       44              
  Lines        1290     1293       +3     
==========================================
+ Hits         1050     1053       +3     
  Misses        240      240

Impacted Files	Coverage Δ
synse/cache.py	83.15% <100%> (+0.27%)	⬆️

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