produce stable diagrams

[nineinchnick]

The sequence image file generated using plantuml is changing on every run. If this file is commited to a repository together with the model it's slightly annoying to see it in diffs of every commit, although the model did not change. This PR switches from using UUIDv4 to a generic UUID that would respect setting a seed.

Added unit tests for generated dfd and seq. Verified additionally using:

$ make report
mkdir -p tm
./tm.py --dfd | dot -Tpng -o tm/dfd.png
./tm.py --seq | java -Djava.awt.headless=true -jar ./plantuml.jar -tpng -pipe > tm/seq.png
./tm.py --report docs/template.md | pandoc -f markdown -t html > tm/report.html
$ cp tm/seq.png tm/seq2.png
$ make report
mkdir -p tm
./tm.py --dfd | dot -Tpng -o tm/dfd.png
./tm.py --seq | java -Djava.awt.headless=true -jar ./plantuml.jar -tpng -pipe > tm/seq.png
./tm.py --report docs/template.md | pandoc -f markdown -t html > tm/report.html
$ md5sum tm/seq.png tm/seq2.png
6c7381e51004ec38bbe4a7522900f37b  tm/seq.png
6c7381e51004ec38bbe4a7522900f37b  tm/seq2.png

[ghost]

DeepCode's analysis on #77ad7d found:

• ❌ 0 critical issues. ⚠️ 0 warnings and 5 minor issues. ✔️ 2 issues were fixed.

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[izar]

Great catch, thanks!