tools: Fix for $LOGNAME missing in Ubuntu 11.10, using $USER instead

Change-Id: I824fc6ca27c2a2308e977a14585afc6dd4996f56
diff --git a/tools/opticharger b/tools/opticharger
index 203fd2b..f8a9d8a 100755
--- a/tools/opticharger
+++ b/tools/opticharger
@@ -25,7 +25,7 @@
 
 if [ "$APKCERTS" = "" ];
 then
-    APKCERTS=$OUT/obj/PACKAGING/target_files_intermediates/$TARGET_PRODUCT-target_files-$TARGET_BUILD_VARIANT.$LOGNAME/META/apkcerts.txt
+    APKCERTS=$OUT/obj/PACKAGING/target_files_intermediates/$TARGET_PRODUCT-target_files-$TARGET_BUILD_VARIANT.$USER/META/apkcerts.txt
     if [ ! -f "$APKCERTS" ];
     then
         echo "Set APKCERTS to the path to your apkcerts.txt file"