Fix CI env vars (heroku#513)

Fixes heroku#414 heroku#504

Move the default cache directories for npm and yarn (heroku#511)

Export cache config vars

Update failure.sh (heroku#510)

Fix typo for grep.

Add metrics for more types of failures (heroku#509)

Add metrics for more types of failures

Dont replace npm because of lockfile if npm is already >= 5 (heroku#499)

Bump default version of Node to Node 8

tweaking

Merge pull request heroku#469 from heroku/manual-yarn-version

manual default for yarn version

Improve error messages when bin version requirements are invalid (her…

…oku#457)

Switch nodejs install over to using nodebin service (heroku#451)

Switch nodejs install over to using nodebin