Ensure staged sessions are not installed in app-staging directory

Since staged session files are stored in /data/app-staging folder, the
existing logic will install the apk in /data/app-staging folder instead
of /data/app. We need to change the logic so that the apk is moved from
/data/app-staging folder to /data/app folder.

Bug: 163037460
Test: atest StagedInstallTest
Change-Id: I51027c138cce6952cd01c7f257a572135f0c3890