done with:

     npm install
     git ls-files | grep -v '\/unstable\/' | xargs ./node_modules/.bin/eclint fix
     git ls-files | grep buildout.hash.cfg | xargs ./update-hash

also drop test_turnserver_promises as promises are now checked by
framework.

Remove method `generateHashFromFiles` in all file `test.py`, import it from `slapos.recipe.librecipe`.

/reviewed-on nexedi/slapos!617