Fix DirichletAlleleDepthAndFraction test to not modify it's expected results.

[cmnbroad]

No description provided.

[cmnbroad]

Rebased on current master, and added a second commit to reflect the new test results that are presumably related to #7394. I assume that the original issue (overwriting the expected results) masked the fact that these test results changed when the tests were run for #7394.

[codecov]

Codecov Report

Merging #7563 (8c5365b) into master (6c6db6e) will decrease coverage by 0.001%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #7563       +/-   ##
===============================================
- Coverage     86.946%   86.945%   -0.001%     
+ Complexity     36929     36928        -1     
===============================================
  Files           2219      2219               
  Lines         173667    173668        +1     
  Branches       18755     18755               
===============================================
- Hits          150996    150995        -1     
- Misses         16057     16058        +1     
- Partials        6614      6615        +1     

Impacted Files	Coverage Δ
...irichletAlleleDepthAndFractionIntegrationTest.java	100.000% <ø> (ø)
.../hellbender/utils/python/PythonUnitTestRunner.java	75.410% <0.000%> (-3.279%)	⬇️

[cmnbroad]

Closing in favor of #7963.