client: make run_isolated_test.py runnable on python3
client: make run_isolated_test.py runnable on python3

but skip failed tests for now.

Bug: 1010816
Change-Id: I2d1918229a7903ca4e5fd609a21e9bd8768ea6e5
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2278905
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

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