Resolve "[scripts] self_test.py: Usage of wrong Reference Executables"

• Related issues: #1171 (closed)
• Requested reviewers: @kiene, @vaclav
• Closes #1171 (closed)

Reason why this change is needed

Fix self_test.py to recognize user-provided paths to reference binaries.

Description of the change

self_test.py recognizes user-provided paths to reference binaries.

Affected operating points

BE.