Do not umount roofs even if it is R/W.

Latest device has rootfs instead of "/system" mount point

Bug: 37737296
Test: adb remount, reboot, and check log
Change-Id: I315ecf71e85255fc55c3a80619920b456bad0956
diff --git a/init/reboot.cpp b/init/reboot.cpp
index e4779c7..17e3576 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -237,7 +237,8 @@
             std::string mount_dir(mentry->mnt_dir);
             // These are R/O partitions changed to R/W after adb remount.
             // Do not umount them as shutdown critical services may rely on them.
-            if (mount_dir != "/system" && mount_dir != "/vendor" && mount_dir != "/oem") {
+            if (mount_dir != "/" && mount_dir != "/system" && mount_dir != "/vendor" &&
+                mount_dir != "/oem") {
                 blockDevPartitions->emplace(blockDevPartitions->begin(), *mentry);
             }
         } else if (MountEntry::IsEmulatedDevice(*mentry)) {