Try to unmount writable filesystems when rebooting

Ext4 filesystems like to be unmounted before rebooting.  The Android system
doesn't have a traditional Linux init setup, and shutting down the system
was not much more than calling sync(2) and reboot(2).  This adds a new
function to libcutils called android_reboot().  By default, it calls sync()
and then remounts all writable filesystems as read-only and marks them clean.
There is a flag parameter in which the caller can ask for sync() not to be
called, or to not remount the filesystems as read-only.  Then it will call
reboot(2) as directed by the other parameters.  This change also updates
adb, init and toolbox to call the new android_reboot() function.
Fixes bugs 3350709 and 3495575.

Change-Id: I16d71ffce3134310d7a260f61ec6f4dd204124a7
diff --git a/init/signal_handler.c b/init/signal_handler.c
index 833e59d..f89d058 100644
--- a/init/signal_handler.c
+++ b/init/signal_handler.c
@@ -23,7 +23,7 @@
 #include <sys/socket.h>
 #include <sys/wait.h>
 #include <cutils/sockets.h>
-#include <sys/reboot.h>
+#include <cutils/android_reboot.h>
 
 #include "init.h"
 #include "list.h"
@@ -96,9 +96,7 @@
                 ERROR("critical process '%s' exited %d times in %d minutes; "
                       "rebooting into recovery mode\n", svc->name,
                       CRITICAL_CRASH_THRESHOLD, CRITICAL_CRASH_WINDOW / 60);
-                sync();
-                __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
-                         LINUX_REBOOT_CMD_RESTART2, "recovery");
+                android_reboot(ANDROID_RB_RESTART2, 0, "recovery");
                 return 0;
             }
         } else {