[CKTest] copy test model to avoid side effects.

[thempel]

Somehow the propagation of the test models
transition matrix induces side effects on the model.

Fixes #1254

[thempel]

@marscher thanks a lot!!

[codecov]

Codecov Report

Merging #1255 into devel will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            devel    #1255      +/-   ##
==========================================
+ Coverage   91.22%   91.23%   +0.01%     
==========================================
  Files         219      219              
  Lines       23766    23767       +1     
==========================================
+ Hits        21681    21685       +4     
+ Misses       2085     2082       -3

Impacted Files	Coverage Δ
pyemma/msm/estimators/lagged_model_validators.py	78.85% <100%> (+0.12%)	⬆️
pyemma/coordinates/transform/vamp.py	91.53% <0%> (+0.38%)	⬆️
pyemma/coordinates/data/util/traj_info_backends.py	92.48% <0%> (+0.93%)	⬆️

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[marscher]

I think we should investigate, which side-effect in MSM actually caused this, since it might be an issue in other spots too.