Use xargs for publishing nuget packages

[jaxxstorm]

Currently we use find for publishing nuget packages. find will only exit with a non 0 error code if you fail to traverse a directory.

This can lead to a situation whereby the nuget package fails to publish, but we never know about it:

find sdk/dotnet/bin/Debug -name 'Pulumi.*.nupkg' | xargs dotnet nuget push -k foobar -s https://api.nuget.org/v3/index.json
echo $?
0

With the addition of the fact that nuget keys expire, we probably need to be notified when nuget publishing fails.

This switches us to use xargs instead

[t0yv0]

Awesome, thanks for this!