init: add even more debugging information for reboot

There are devices stuck waiting for vendor_init to finish a command,
without giving much more information.  Instead of setting aside the
last run command, it's more valuable to store and dump the last 30
logs seen.

Bug: 155203339
Test: these logs appear during hung reboots
Test: normal reboots have no difference.
Change-Id: I99cae248eb81eaf34ef66b910fa653a9fa135f68