Make apk session commit during pre-reboot verification asynchronous

This breaks down existing pre-reboot verification logic into multiple
states and arrange them in a linear order. Each state is triggerred by a
message.

Bug: 137282250
Test: atest CtsStagedInstallHostTestCases
Test: atest RollbackTest
Change-Id: I17c1c5e43a631d7c061413556f419244ffc276db
1 file changed