[cipd] Add t.Parallel() to common tests
[cipd] Add t.Parallel() to common tests

R=vadimsh@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2653613005

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