Implement Reboot bootloader via bootloader_message

- Write reboot bootloader message to misc
 - Clarify naming for reboot to recovery

BUG: https://issuetracker.google.com/issues/32474515

Change-Id: I4e42509bfcf572e37c8fc070d6571afe406a48b6
Signed-off-by: Vineela Tummalapalli <vineela.tummalapalli@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Reviewed-on: https://android.intel.com/548494

init/builtins.cpp

@@ -703,6 +703,15 @@ static int do_powerctl(const std::vector<std::string>& args) {
             callback_on_ro_remount = unmount_and_fsck;
         } else if (cmd == ANDROID_RB_RESTART2) {
             reboot_target = &command[len + 1];
+            // When rebooting to the bootloader notify the bootloader writing
+            // also the BCB.
+            if (strcmp(reboot_target, "bootloader") == 0) {
+                std::string err;
+                if (!write_reboot_bootloader(&err)) {
+                    LOG(ERROR) << "reboot-bootloader: Error writing "
+                                  "bootloader_message: " << err;
+                }
+            }
         }
     } else if (command[len] != '\0') {
         LOG(ERROR) << "powerctl: unrecognized reboot target '" << &command[len] << "'";