Include keyspace range checks on flow tests

[filipecosta90]

Up until now we didn't really checked the keyspace range after write tests. This PR introduces it.
I noticed that due to the PR #206 having a but and precisely increasing the keyspace range.

[codecov-commenter]

Codecov Report

Merging #208 (31cb241) into master (82dba6a) will increase coverage by 1.07%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##           master     #208      +/-   ##
==========================================
+ Coverage   55.90%   56.97%   +1.07%     
==========================================
  Files          21       21              
  Lines        4270     4270              
==========================================
+ Hits         2387     2433      +46     
+ Misses       1883     1837      -46     

Impacted Files	Coverage Δ
run_stats.cpp	78.28% <0.00%> (+0.26%)	⬆️
obj_gen.cpp	47.75% <0.00%> (+1.96%)	⬆️
client.cpp	63.44% <0.00%> (+2.11%)	⬆️
memtier_benchmark.cpp	53.03% <0.00%> (+3.44%)	⬆️
client.h	66.66% <0.00%> (+4.16%)	⬆️

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