Don't resume uncommitted sessions.

The "isCommitted" bit wasn't previously carried over since before staged
install a session successfully commited was promptly destroyed.
Checkpoint also the commit status and carry it over.

Fix: 128432016
Test: reproduced the bug with a hack on StagedRollbackTest and verified
it doesn't trigger anynmore after the change.

Change-Id: I948fd3d964800621f5d5f5019621839383d6b486