chore(utils/crypto_ecc): Improve structure of EdDSA tests

The new tests structure puts the test cases in charge of setting up their test
environment and cleaning it up afterwards. This avoids dependancies between the
test cases and is a best practise followed by many test frameworks.

Closes #1
Merge pull request #2 from vsaw/chore/1-test-util-crypto-eddsa

chore(utils/crypto_ecc): Improve structure of EdDSA tests