Skip update verification if care_map is not found

Recently flashed devices may not have care_map.txt in /data/ota_package.
This leads to a failure of update-verifier and prevents boot
success flag from being set. So, we need to skip verification
in case the file is not found.

Error message:
... I update_verifier: Started with arg 1: nonencrypted
... I update_verifier: Booting slot 1: isSlotMarkedSuccessful=0
... E update_verifier: Care map /data/ota_package/care_map.txt not found.
... E update_verifier: Failed to verify all blocks in care map file

Bug: 30156449
Change-Id: Ia15f5f3e7ca2ea6981d49678e799b9f70d134faa