CI does not run all the RPC tests

[cburgdorf]

What is wrong?

As I added CI testing for Istanbul in #1749 I noticed the job takes quite a while to run. Upon further inspection I noticed most of our other rpc-state-something jobs only run one single test! I thought I must have screwed something up in the PR that dropped Python 3.6 support but it turns out these jobs have been executing only a single job for quite a while (Here's a run from 1 month ago)

How can it be fixed

🤷‍♂️

[cburgdorf]

Uh, and I guess it's my fault. It's been like that ever since we upgraded the fixture submodule last time in #1255

It looks like something changed there about the structure of the tests so that we only catch Istanbul tests. It works for Py-EVM though, need to look what we are doing differently there...

[cburgdorf]

Ok, it looks like what happened is that Py-EVM started running the tests out of fixture/BlockchainTests in ethereum/py-evm#1577 while Trinity runs them differently but I'm still figuring out how exactly.

[cburgdorf]

This was done by #1756