init: replace panic() with LOG(FATAL)

Test: boot bullhead
Test: Introduce LOG(FATAL) at various points of init and ensure that
      it reboots to the bootloader successfully
Test: Introduce LOG(FATAL) during DoReboot() and ensure that it reboots
      instead of recursing infinitely
Test: Ensure that fatal signals reboot to bootloader

Change-Id: I409005b6fab379df2d635e3e33d2df48a1a97df3
diff --git a/init/reboot.h b/init/reboot.h
index e559540..8586556 100644
--- a/init/reboot.h
+++ b/init/reboot.h
@@ -22,6 +22,9 @@
 namespace android {
 namespace init {
 
+// This is a wrapper around the actual reboot calls.  DoReboot() should be preferred in most cases.
+void __attribute__((noreturn)) RebootSystem(unsigned int cmd, const std::string& rebootTarget);
+
 /* Reboot / shutdown the system.
  * cmd ANDROID_RB_* as defined in android_reboot.h
  * reason Reason string like "reboot", "userrequested"