Theano-PyMC compatibility updates

[brandonwillard]

This PR fixes some compatibility issues introduced by recent changes in Theano-PyMC.

[brandonwillard]

FYI: These tests won't pass until we cut the next release of Theano-PyMC, since the updates this PR targets aren't released yet.

[Sayam753]

Hi @brandonwillard

I was running test suite locally on this PR with theano-pymc@master. And pymc3/tests/test_ode.py::test_logp_scalar_ode failed with AttributeError: 'DifferentialEquation' object has no attribute '_get_test_value'.

So, looking upon the PR pymc-devs/Theano-PyMC#112, these lines need to be refactored as well.

https://github.com/pymc-devs/pymc3/blob/0b0797011c0c8023743aaf94dd0016e001191c17/pymc3/ode/ode.py#L165-L167

I think this has to deal with new theano.gof.get_test_value function.

[codecov]

Codecov Report

Merging #4218 (3ea99ac) into master (0b07970) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4218   +/-   ##
=======================================
  Coverage   88.94%   88.95%           
=======================================
  Files          92       92           
  Lines       14800    14806    +6     
=======================================
+ Hits        13164    13170    +6     
  Misses       1636     1636           

Impacted Files	Coverage Δ
pymc3/distributions/dist_math.py	91.82% <100.00%> (+0.03%)	⬆️
pymc3/distributions/multivariate.py	81.12% <100.00%> (-0.08%)	⬇️
pymc3/model.py	89.36% <100.00%> (+0.02%)	⬆️
pymc3/ode/ode.py	93.81% <100.00%> (+0.06%)	⬆️
pymc3/tests/helpers.py	60.34% <100.00%> (+3.74%)	⬆️

[twiecki]

Thanks @brandonwillard and @Sayam753!