Test helpers scripting

type:none

For this to work: remove all tests with some printed variable (gen#42..) 😞

how to use:

1. uncomment line 6 in src/bin/expect_tests/dune
2. ./scripts/test_expect.sh list will list all expect tests (around 800)
3. ./scripts/test_expect.sh 6 execute test number 6 ..
4. dune promote if needed, and go back to 2.