Enable filesystem checkpoint for staged apk installation

Because: We want to make multiple staged sessions' installation
atomic. This behaviour is consistent with what we do with apex
packages.

File system checkpoint will be enabled during the end-phase of
pre-reboot verification of staged session. On reboot, if anything goes
wrong during apk installation, we reboot again to enter rollback-mode.
On rollback-mode, we mark all active staged session as failed.

The new implementation is unaware of its surrounding sessions, i.e,
when a session fails we have no way to know if there is any other
staged session which was applied on this boot. As such, whenever a
session fails, we reboot immediately to revert back to safe state.

Bug: 141843321
Test: atest StagedInstallTest#testInstallMultipleStagedSession_PartialFail_ApkOnly
Change-Id: I1619c6f113fc0b07f2c69215683e4964e0e99458