[swarming] use go isolated when cipd is enabled by default
[swarming] use go isolated when cipd is enabled by default

I want to see this on dev today and deploy to prod tomorrow if it looks
good.

Bug: 932396
Change-Id: I496f7baee8209462bf66446519197bc591fedc80
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1997521
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py