reboot_utils: Check bootconfig for reboot parameters

Androidboot parameters have moved from /proc/cmdline to /proc/bootconfig
so we need to check both places in reboot_utils.
"ro.boot.*" properties can not be used because this is initialized
before the properties are set.

Test: boot Cuttlefish with init_fatal_panic and
init_fatal_reboot_target in bootconfig and in cmdline
Bug: 191494101

Merged-In: I6c230496ec1c3632470d20ff4a31f28db96ea71b
Change-Id: I6c230496ec1c3632470d20ff4a31f28db96ea71b