Make number of series a property of prop test

[justinjc]

Follow up from PR #2128 (comment)

[prateek]

LGTM w/ a nit

[codecov]

Codecov Report

Merging #2130 into master will increase coverage by 18.3%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2130      +/-   ##
==========================================
+ Coverage    51.1%    69.4%   +18.3%     
==========================================
  Files         773     1012     +239     
  Lines       62300   130262   +67962     
==========================================
+ Hits        31844    90443   +58599     
- Misses      28273    33734    +5461     
- Partials     2183     6085    +3902

Flag	Coverage Δ
#aggregator	80.8% <ø> (-19.2%)	⬇️
#cluster	68.1% <ø> (-31.9%)	⬇️
#collector	64.8% <ø> (+32.1%)	⬆️
#dbnode	77.9% <ø> (+3.1%)	⬆️
#m3em	72.5% <ø> (-27.5%)	⬇️
#m3ninx	69.8% <ø> (-30.2%)	⬇️
#m3nsch	59.6% <ø> (-40.4%)	⬇️
#metrics	17.6% <ø> (-82.4%)	⬇️
#msg	74.7% <ø> (-25.3%)	⬇️
#query	49.9% <ø> (-50.1%)	⬇️
#x	82.5% <ø> (-17.5%)	⬇️

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