[restrict_nonpreloads_system_shareduids] prevent previously installed apps...

[restrict_nonpreloads_system_shareduids] prevent previously installed apps from being uninstalled on reboots

Change the restriction to be applied to non-boot installations only.
That way, previously installed apps won't be uninstalled due to the
restriction.

Steps to repro the original issue:

1) Change the restriction condition to a persisted system property for
   easy debugging
2) set the property to false to disable the restriction
3) m HelloWorldSettings2
4) adb install /sdb/main/out/target/product/oriole/testcases/HelloWorldSettings2/arm64/HelloWorldSettings2.apk
5) verify that the test app is installed
6) enable the property and verify that new installs of the same app will be
   rejected
7) reboot
8) observe that the app's apk directory is removed after reboot

Flag: android.content.pm.restrict_nonpreloads_system_shareduids
BUG: 346687234
Test: manual by repeating the steps above but check that with this CL,
the app will no longer be deleted after reboot

Change-Id: Ic7e655b94e023fb41b6c49c164fc7ad1ec461a58