[run_isolated.py] fix bogus comment.
[run_isolated.py] fix bogus comment.

Introduced by https://codereview.chromium.org/2710153006/.

R=maruel@chromium.org, vadimsh@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2711383003

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