OMS: stabilize unit tests

- Add hasCode=false to overlay packages as a workaround for b/124375490

- Sprinkle Thread.sleeps in InstallOverlayTests in an attempt to make
  the tests less flakey when executed on emulator

Test: atest OverlayDeviceTests OverlayHostTests
Change-Id: I745a8477ed5e72db572737a0af0e59478893e42b
13 files changed