client: store content only when valid in fake server
client: store content only when valid in fake server

Bug: 1071740
Change-Id: I2ce49c14f33c8f3b6d5ab6ae17f1dff58b53f365
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2156234
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Ye Kuang <1cd89f22f3967fc3dcb883b53940be4b98ec483f@google.com>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Ye Kuang <1cd89f22f3967fc3dcb883b53940be4b98ec483f@google.com>

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