Prefix unit tests in device_sync with "DeviceSync"

Add the prefix "DeviceSync" to all unit tests in the
chromeos/service/device_sync directory so all tests can be run with
--gtest-filter="DeviceSync*".

Bug: 899080
Change-Id: I0ed1124daa853da2c4ebecd2ec229dbcf5fea7bf
Reviewed-on: https://chromium-review.googlesource.com/c/1495796
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Josh Nohle <nohle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636569}
7 files changed