Merge "Don't abandon child sessions (1/n)" into qt-dev

                if (age >= MAX_SESSION_AGE_ON_LOW_STORAGE_MILLIS) {

                    // Aggressively close old sessions because we are running low on storage

                    // Their staging dirs will be removed too

                    session.abandon();

                    PackageInstallerSession root = !session.hasParentSessionId()

                            ? session : mSessions.get(session.getParentSessionId());

                    if (!root.isDestroyed() && 

                            (!root.isStaged() || (root.isStaged() && root.isStagedSessionReady()))) 

                    {

                        root.abandon();

                    }

                } else {

                    // Session is new enough, so it deserves to be kept even on low storage

                    unclaimedStagingDirsOnVolume.remove(session.stageDir);