[bbagent] Properly fill KnownGerritHosts.
[bbagent] Properly fill KnownGerritHosts.

This was added to host.Options, but never wired up in bbagent!

R=ihuh@google.com, 9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org, yiwzhang@google.com

Bug: 1015181
Change-Id: Ibb11bcae1515f26ebd721450239f9264031c9060
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2347127
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Auto-Submit: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

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