Use annotation for tests that require a device

Currently all flicker tests run on a physical devices.

In the future, some flicker tests may run on a physical devices
and others may run on virtual devices for scalability. In this CL
we use the "RequireDevice" annotation to indicate which tests should
run on device

Test: atest FlickerTests
Change-Id: I472c30612535310265717a5ae420feb534159c41