Update cloud implementation w/ new datastore API
Update cloud implementation w/ new datastore API

The cloud datastore API has been updated. Update the cloud datastore
layer implementation accordingly.

BUG=None
TEST=None
R=iannucci@chromium.org

Review-Url: https://codereview.chromium.org/2492103003

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