Set a cap while package manager is dumping the critical info

Also, log 'Relax SCAN_REQUIRE_KNOWN' to the system log instead.
It would be logged each time when the device boot-up, and the device
could suffer from message bloat.

Bug: 120549172
Test: adb push a large file to /data/system/uiderrors.txt; \
      adb shell dumpsys package
Change-Id: Ie7114a701b397ffe2ee98faf4ead8ac5633c09c7