Ignore abandon after install relinquished.

We recently changed the install flow to fully dexopt before renaming
the staging directory.  This exposed the ability for the session owner
to abandon and destroy the stage contents while dexopt was still
happening.

Due to SELinux rules, the abandon would fail to clean up the stage
directory, and PackageManager would "successfully" rename and install
that stage, which now only contained the oat/ directory.

To avoid this case, we now ignore abandon requests once we've passed
the "point of no return" and relinquished our stage over to
PackageManagerService.

Bug: 20175072
Change-Id: I4ad5b1eba0e38f1315b8330bd95be6e3bc6c635a