Use "sys.isolated_storage_snapshot" prop to check for the feature.

StorageManager.hasIsolatedStorage() has already been updated to use
this, so most callers are already using this sys prop. Now, updating
remaining callers to use it as well.

Bug: 122559151
Test: manual
Change-Id: I1e48c00d21d98a47c6625cdf62d0ab69304e03e5
diff --git a/core/jni/com_android_internal_os_Zygote.cpp b/core/jni/com_android_internal_os_Zygote.cpp
index a8e1427..59aab46 100644
--- a/core/jni/com_android_internal_os_Zygote.cpp
+++ b/core/jni/com_android_internal_os_Zygote.cpp
@@ -86,6 +86,7 @@
 static pid_t gSystemServerPid = 0;
 
 static const char kIsolatedStorage[] = "persist.sys.isolated_storage";
+static const char kIsolatedStorageSnapshot[] = "sys.isolated_storage_snapshot";
 static const char kZygoteClassName[] = "com/android/internal/os/Zygote";
 static jclass gZygoteClass;
 static jmethodID gCallPostForkSystemServerHooks;
@@ -530,7 +531,7 @@
         return true;
     }
 
-    if (GetBoolProperty(kIsolatedStorage, false)) {
+    if (GetBoolProperty(kIsolatedStorageSnapshot, GetBoolProperty(kIsolatedStorage, false))) {
         if (mount_mode == MOUNT_EXTERNAL_FULL) {
             storageSource = "/mnt/runtime/write";
             if (TEMP_FAILURE_RETRY(mount(storageSource.string(), "/storage",