For n_jobs, close client before tearing down cluster

[rwedge]

Should fix #852

Shutting down the dask scheduler before the client occasionally caused "Connection closed" errors to pop up. Shutting down the client first seems to resolve this problem.

[kmax12]

Codecov Report

Merging #853 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #853   +/-   ##
=======================================
  Coverage   98.14%   98.14%           
=======================================
  Files         117      117           
  Lines       10812    10812           
=======================================
  Hits        10611    10611           
  Misses        201      201           

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[codecov-io]

Codecov Report

Merging #853 into master will not change coverage.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master     #853   +/-   ##
=======================================
  Coverage   98.14%   98.14%           
=======================================
  Files         117      117           
  Lines       10812    10812           
=======================================
  Hits        10611    10611           
  Misses        201      201

Impacted Files	Coverage Δ
...computational_backends/calculate_feature_matrix.py	98.58% <50%> (ø)	⬆️

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