Yeah, this a similar issue to the one which the users on AskDifferent (linked above 
) were dealing with. Installing your own version of OpenSSL doesn’t change the system version, and $ brew link won’t fix that.
From reading about on the home-brew github docs, $ brew link is intended to link your custom installation (OpenSSL 1.0.2j here), with any other Homebrew builds which may require OpenSSL. However, Homebrew won’t usurp the system installation (which is good- that will cause problems).
Since you need to use home-brew’s version in a non-homebrew software (Trellis), you’ll either have to (as I said before) rename the system OpenSSL directory and create a symlink to the brew OpenSSL directory- or, much much more advisable I now realise, tweak the playbook to use the brew version, or try any of the methods outlined in the brew docs.
Ultimately it’s not a problem with home-brew, but it may be something worth submitting as a bug to the Trellis github.