Use Shouldly in AssertLogDoesntContain
Use Shouldly in AssertLogDoesntContain

This will improve the error message when the assertion fails, which is currently

```
Assert.Equal() Failure
Expected: -1
Actual: 0
```

AndyGerlicher/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,mono/msbuild,cdmihai/msbuild,Microsoft/msbuild,rainersigwald/msbuild,mono/msbuild,mono/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,cdmihai/msbuild,Microsoft/msbuild,jeffkl/msbuild,jeffkl/msbuild,chipitsine/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,mono/msbuild,Microsoft/msbuild,Microsoft/msbuild,cdmihai/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,chipitsine/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,chipitsine/msbuild