Omit libraries and tests from tools coverage numbers

[theotherjimmy]

I noticed recently, that our coverage numbers changed when we updated a
package we depend on. This is nonsense. Our coverage numbers should
reflect only our code.

[0xc0170]

Who else should review this change? How to compare between previous vs this patch?

[theotherjimmy]

@0xc0170 Uh, you should be able to run the coverage yourself with coverage run -m pytest tools/test && coverage report from the root of this repo. If you do that on master, you will see coverage numbers for the tests themselves, which are generally 100%. If you run the coverage report from this PR, then you will not see the coverage numebers for the tests.