Rotate logs on every boot

Currently, recovery-persist only rotates the logs if it can parse
/sys/fs/pstore/pmsg-ramoops-0 . Change this behavior to always rotate
last kernel log if present. This helps collect more debug logs when
troubleshooting boot failures.

Test: reboot device, make sure logs are rotated
Change-Id: I41da2eda3c6c241e90208af888e9e35bec0474fe