Fix support for absolute and relative paths TestCase.purge_optional()

[tysmith]

No description provided.

[codecov]

Codecov Report

Merging #259 (a295b6a) into master (9fe18b9) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #259      +/-   ##
==========================================
- Coverage   99.24%   99.24%   -0.01%     
==========================================
  Files          49       49              
  Lines        5199     5191       -8     
==========================================
- Hits         5160     5152       -8     
  Misses         39       39              

Impacted Files	Coverage Δ
grizzly/common/runner.py	100.00% <100.00%> (ø)
grizzly/common/storage.py	100.00% <100.00%> (ø)

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