Do not use PackageManagerHelper created on boot for LoaderTask.

This CL partially reverts ag/26827295.

Re-using the PackageManagerHelper obj created earlier than LoaderTask obj will lead to the bug where private space user handle is not recognized. This is a temporary fix to create a separate PackageManagerHelper obj for LoaderTask. The real fix should be on framework side.

Also note that PackageManager service instance is now created much later in launcher lifecycle than before.

Fix: 338091143
Test: manual
Flag: NONE
Change-Id: Iab467fe8979aec52c5837c8fd676f821b2e3eb3c