first_stage_init: add hook to exec a shell script

If the first stage console is being used, attempt to run /first_stage.sh
immediately before the console is created.

Bug: 154126020
Change-Id: I8b7431e7b8219afea295b120d7ea91751804bda6
Merged-In: I8b7431e7b8219afea295b120d7ea91751804bda6
5 files changed