Fix ignoring arguments passed to save_model.

[peterscherpelz]

Before this change, defaults were passed to _save_model, rather than the
correct arguments the user supplied to save_model.

[codecov]

Codecov Report

Merging #938 (46359d6) into devel (3e19a85) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            devel     #938      +/-   ##
==========================================
- Coverage   54.59%   54.56%   -0.03%     
==========================================
  Files         211      210       -1     
  Lines       21564    21527      -37     
  Branches     2891     2888       -3     
==========================================
- Hits        11772    11747      -25     
+ Misses       9240     9228      -12     
  Partials      552      552              

[ekalosak]

This looks good - to merge, we need a test that covers this code. That'll keep us from making the same mistake in the future. Please let me know if you need any help writing the test. I don't think it will be too onerous :)