Chloe Kudryavtsev authored May 16, 2019 and TBK committed May 24, 2019

Superseeds PR7880 (there was too much to change for a review).

1. Caddy now uses the Go Modules system:
    -> builds and tests require a new environment variable
    -> it now requires a custom cleanup step
2. Tests now pass (on my builder)
3. Adopt

Closes: GH-7907