Add a token for "Build is failing"

[costateixeira]

Can be generated and consumed by tempaltes

[lmckenzi]

@costateixeira will try to prototype how this would work. Because successful build content is copied on a default build, it won't be possible to do this by putting a special file in the build on a success (because the copy would always be a success). Instead, the process will have to go look in other folders to see if there was a more recent failure.