devtools: fix GO_DISCOVERY_DOCKER_* comparisons
devtools: fix GO_DISCOVERY_DOCKER_* comparisons

If GO_DISCOVERY_DOCKER_* is not set, the default value should be false
not true, which is now fixed.

Change-Id: I06968a96e9ff363862b3df60be88cbac6d2d7be1
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/339230
Trust: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Run-TryBot: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite