Parts of the test suite could be exposed for downstream use

[veox]

• py-evm Version: v0.2.0-alpha.42-112-g5c080532 (current master, commit 5c08053)
• OS: IRRELEVANT
• Python Version (python --version): IRRELEVANT
• Environment (output of pip freeze): IRRELEVANT

What is wrong?

Some utilities, such as the infamous INCORRECT_UPSTREAM_TESTS, but also helpers to select fixture by VM rules (a.k.a. fork), have been copy-pasted between py-evm and trinity since the repo split.

In ethereum/trinity#608, these were marked with TODOs:

• https://github.com/ethereum/trinity/pull/608/files#diff-08fccd373dc59fca958451434197a951R107
• https://github.com/ethereum/trinity/pull/608/files#diff-08fccd373dc59fca958451434197a951R213

How can it be fixed

Move them to somewhere in eth.tools.fixtures?.. Don't know, really.