cipd: Make Destination implementation concurrency safe.
cipd: Make Destination implementation concurrency safe.

Destination abstracts a place where zip file is being extracted.

R=iannucci@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2652593002

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