Fixes a black flash that occurred when the device was docked
because the UiModeManagerService was launching the Somnambulator
to start the dream when docked. This caused an unnecessary
activity transition and could in fact make dreaming less
reliable than if the UiModeManagerService started the dream itself.
Moved common code from UiModeManagerService and Somnambulator
to Sandman to ensure it is kept in sync.
Bug: 7328545
Change-Id: I46102784e2ab1acc0241d43a48abf0581278af24
11159e9a78