Keep finalized staged sessions in session database

Finalized staged sessions, i.e. sessions that are in
isStagedSessionApplied and isStagedSessionFailed should be kept in the
session database to allow inspection. Presently, a call to abandon() on
a session in finalized state causes it to be removed from the database.

Bug: 131290871
Test: atest CtsStagedInstallHostTestCases (see CL in same topic)
Change-Id: I6860ea5b2501c992504c7434bb4988b58dacfe52