Fix to allow for hotstarting with systemStepExact=False

[zhang-alvin]

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Description

Addresses #1235. Not setting the model time prior to proceeding with calculation leads to an infinite loop.

Thanks @cekees for the suggested fix.

Added a test within tests/TwoPhaseFlow to test for the fix. Note to keep in mind is that the test is to avoid changes to the infinite loop fix.

I tried setting a test to compare numerical results but I believe something along the lines of #1184 was causing a different behavior between the directory-level pytest call and a make test call at the root.

[codecov]

Codecov Report

Merging #1236 into master will decrease coverage by 0.00%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #1236      +/-   ##
==========================================
- Coverage   52.74%   52.74%   -0.01%     
==========================================
  Files         531      531              
  Lines      109533   109536       +3     
==========================================
  Hits        57777    57777              
- Misses      51756    51759       +3     

Impacted Files	Coverage Δ
proteus/tests/TwoPhaseFlow/test_TwoPhaseFlow.py	85.48% <ø> (ø)
proteus/tests/TwoPhaseFlow/damBreak.py	89.39% <66.66%> (-1.24%)	⬇️
proteus/NumericalSolution.py	70.76% <100.00%> (+0.02%)	⬆️
proteus/tests/test_boundaryconditions.py	97.33% <0.00%> (-0.25%)	⬇️

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[zhang-alvin]

@cekees, I think the line in NumericalSolution is causing a massive code cov decrease. I can try moving the line elsewhere or is there some simpler fix to the drop in coverage.

I think @ejtovar ran into something similar pretty recently. I forget how it was resolved.

[zhang-alvin]

For reference, prior to hack/removal of test, codecov indicated -36% coverage.
Removing test yields only a -0.01% drop.
Going to turn the test back on to see if behavior is corrected.