add v8-canary builds to www setup

[rvagg]

some chakracore stuff in there too that's come in from an upstream sync

[joaocgreis]

For reference, the ChakraCore changes had been in #547 , I didn't land them because I wanted to keep it more dynamic, but it's been there for a while and there's no harm in landing either.

[joaocgreis]

@rvagg looking at https://github.com/nodejs/build/pull/547/files , user.yaml has two entries: dist and staging directories. Isn't this PR missing the staging one?

[rvagg]

fixed the problem in user.yml that @joaocgreis pointed out and merged it