Basic process isolated tests for randomness generation

[torben-hansen]

Issues:

Resolves #ISSUE-NUMBER1
Addresses #ISSUE-NUMBER2

Description of changes:

Describe AWS-LC’s current behavior and how your code changes that behavior. If there are no issues this pr is resolving, explain why this change is necessary.

Call-outs:

Point out areas that need special attention or support during the review process. Discuss architecture or design changes.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 89.33333% with 16 lines in your changes missing coverage. Please review.

Project coverage is 79.05%. Comparing base (e0afb8a) to head (7b04d4c).

Files with missing lines	Patch %	Lines
crypto/fipsmodule/rand/rand_isolated_test.cc	89.62%	8 Missing and 3 partials ⚠️
crypto/test/test_util.cc	50.00%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           randomness_generation    #2255      +/-   ##
=========================================================
+ Coverage                  79.02%   79.05%   +0.02%     
=========================================================
  Files                        628      629       +1     
  Lines                     107215   107353     +138     
  Branches                   15161    15168       +7     
=========================================================
+ Hits                       84729    84868     +139     
+ Misses                     21773    21767       -6     
- Partials                     713      718       +5     

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