Sdk: dotnet publish fail on warnings

[SusLes]

Moving issue here from Dotnet.
Issue entered by ChaosCA.
https://github.com/Microsoft/dotnet/issues/799

Full Text from issue:
Hey there,
I apologies if this is the wrong place. This is more of a feature suggestion to have a flag on the dotnet publish command that causes it to exit with a non-zero status code when it encounters a warning.
This is useful for CI/CD applications that are unmanaged, failing on warnings can prevent potentially buggy code from reaching production when it otherwise may have not be caught. Sort of like a strict mode.

[braunsonm]

Thanks @SusLes!

[nguerrera]

This is already possible:

dotnet publish /p:TreatWarningsAsErrors=true /warnaserror

More on how this works:

1. $(TreatWarningsAsErrors) is passed to the compiler (and other tools) run during the build.
2. /warnaserror will make other MSBuild warnings into errors as well