client: run chown if file is not owned by swarming user
client: run chown if file is not owned by swarming user

This is to make file/dir movable to local cache directory.

Bug: 986676
Change-Id: Ib2b1219a4915d1777c73e31fd4641938129edb41
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2262085
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