Put sessionmaker code in a function

[stveit]

Fix for #226

The downside of this code is that the sessionmaker will be created every time sqla_session is called. If wanted, I can remedy this by setting Session as a global variable and only allowing it to be set once or something

[codecov]

Codecov Report

Merging #227 (8c8f90e) into develop (739e933) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #227      +/-   ##
===========================================
+ Coverage    59.41%   59.44%   +0.02%     
===========================================
  Files           61       61              
  Lines         6180     6184       +4     
===========================================
+ Hits          3672     3676       +4     
  Misses        2508     2508              

Impacted Files	Coverage Δ
src/cnaas_nms/db/session.py	76.92% <100.00%> (+1.92%)	⬆️

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[hmpf]

Fix for #226

The downside of this code is that the sessionmaker will be created every time sqla_session is called. If wanted, I can remedy this by setting Session as a global variable and only allowing it to be set once or something

It's so little code why not just do it. I assume you mean a global in the same module? (I wonder if this has a name besides "Singleton".) Though, might be useful to have a way to check that the session has not disconnected and then reconnect.. but that is probably out of scope.