update_verifier: correct group in rc file

update_verifier should be in the cache group, not 'class'.

Also use PLOG instead of LOG if care_map.txt cannot be opened.

Bug: 36818743
Test: boot sailfish
Test: fake OTA on sailfish and verify update_verifier reads care_package
Change-Id: I0ec844cac5ef5c63b18ebee90160854fd84ee829