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/service.cpp b/init/service.cpp
index 1b5cc19..c201ec9 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -306,8 +306,7 @@
     if ((flags_ & SVC_CRITICAL) && !(flags_ & SVC_RESTART)) {
         if (now < time_crashed_ + 4min) {
             if (++crash_count_ > 4) {
-                LOG(ERROR) << "critical process '" << name_ << "' exited 4 times in 4 minutes";
-                panic();
+                LOG(FATAL) << "critical process '" << name_ << "' exited 4 times in 4 minutes";
             }
         } else {
             time_crashed_ = now;