Mark boot completion via apexservice

Use the StagingManager lifecycle class to call into ApexManager
when the boot completed broadcast is received. ApexManager will
then call into apexservice to inform apexd of the boot completion,
instead of apexd relying on the sys.boot_completed property.

Test: atest StagedInstallTest
Test: atest ApexRollbackTests
Bug: 158467962
Change-Id: Ibcb4cb784243530eb2cf8c2633651342e8115d14