Bring back ADB_EXTERNAL_STORAGE.

Bug: 7119408
Change-Id: Ia08146965ee6218a033a70c2f02cbc621e339316
diff --git a/init.tuna.rc b/init.tuna.rc
index a55d833..530330f 100755
--- a/init.tuna.rc
+++ b/init.tuna.rc
@@ -6,6 +6,7 @@
     mkdir /storage/sdcard0 0000 root root
 
     export EXTERNAL_STORAGE /storage/sdcard0
+    export ADB_EXTERNAL_STORAGE /mnt/shell/sdcard0/0
     export MULTIUSER_EXTERNAL_STORAGE /mnt/shell/sdcard0
 
     # Support legacy paths