Squash runnables in onBootCompleted (1/n)

Some code clean-up to makes it easier to register
OnPropertiesChangedListener there in the next patch.

Bug: 147712943
Test: atest StagedRollbackTest RollbackTest
Change-Id: I46d08fe2715b7c6a08d9a6d862dc0ab0dd3de12c
1 file changed