Unify testing code style

[nventuro]

Some test suites are a bit all over the place, we should make them more consistent. Current items:

• use const and let in favor of var
• await instead of .then
• chai.should instead of assert
• this to store global variables (Use this in tests #1200)
• remove chai-as-promised
• use (await promise).should.bla instead of assigning and testing (Await and test instead of assigning #1201)
• add names (e.g. owner) to accounts
• remove arrow functions where they shouldn't be used (Remove arrow functions in tests #1202)
• use expectEvent to test logs-related stuff (Use expectEvent to test logs #1232)

[frangio]

Also using this to store test state instead of global(ish) variables.

[nventuro]

We should also remove chai-as-promised, since it doesn't work properly when combined with chai-bignumber, is not being maintained, and can be replaced by (await promise) anyway.

[frangio]

I added an item about arrow functions. There is a section in the Mocha website about them. I could find incorrect use of arrow functions in the tests for: Superuser, ECRecovery, RBAC, and SignatureBouncer.

@nventuro Not sure if we should also open an issue for this. Are you tracking each item separately also?

[nventuro]

Tbh I'm not doing great work at handling this, I should've opened separate issues (and maybe a meta-issue?). Thanks for the bit about arrow functions!

[nventuro]

This should be easier to track now.

[nventuro]

This is now ready, thanks @jacobherrington, @justuswilhelm and @Aniket-Engg! 🎉