[resultui] enable https in karma test runner
[resultui] enable https in karma test runner

Some part of the code assumes that the site is host on HTTPS.
This helps us test requests with relative URLs.

R=gavinmak@google.com, nodir

Change-Id: I803702a71349e2614b998ebe0e5cbce7d40cb193
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2959934
Auto-Submit: Weiwei Lin <968518a24f41fef00b747498600e52b792d06ae0@google.com>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go