Fix PackageManagerService crashed due to NPE during debugging installing

Symptom:
PackageManagerService crashed due to NPE during debugging installing
an invalid package. The crash can be observed only when DEBUG_INSTALL
flag is true.

Root cause:
In this case, the null object access occurs during debug output.

Solution:
Avoid directly accessing packageName. Show the package name via
toString() of Package object.

Bug: 140057579
Change-Id: I302903a2a6b29454dbf718a07c82f5583f93097c