Adding tests for BoltzWann (at least for the electrical conductivity)

[giovannipizzi]

I'm adding a simple test to begin with since I got a bug report that I cannot reproduce - by running this also in the test farm, as soon as it's merged, I can check if the problem surfaces on some compiler only

[codecov]

Codecov Report

Merging #282 into develop will increase coverage by 1.78%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop    #282      +/-   ##
==========================================
+ Coverage    63.32%   65.1%   +1.78%     
==========================================
  Files           29      29              
  Lines        17984   17767     -217     
==========================================
+ Hits         11388   11567     +179     
+ Misses        6596    6200     -396

Impacted Files	Coverage Δ
src/postw90/geninterp.F90	69.23% <0%> (-5.77%)	⬇️
src/postw90/postw90_common.F90	62.87% <0%> (-5.76%)	⬇️
src/io.F90	67.53% <0%> (-2.82%)	⬇️
src/wannier_prog.F90	80.99% <0%> (-0.98%)	⬇️
src/parameters.F90	81.22% <0%> (-0.76%)	⬇️
src/postw90/kslice.F90	68.4% <0%> (-0.49%)	⬇️
test-suite/library-mode-test/test_library.F90	64.7% <0%> (-0.35%)	⬇️
src/postw90/postw90.F90	84.33% <0%> (-0.19%)	⬇️
src/postw90/kpath.F90	63.53% <0%> (-0.16%)	⬇️
src/postw90/dos.F90	79.16% <0%> (+2.38%)	⬆️
... and 2 more

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