Only cache sudo if outside chroot

src/scripts/image_to_usb.sh

Index: src/scripts/image_to_usb.sh
diff --git a/src/scripts/image_to_usb.sh b/src/scripts/image_to_usb.sh
index 3744ac08260510bfe5249079c8b73c36f17c7649..2cba18aae4d7821c4ee8f2ff9252e495f1646072 100755
--- a/src/scripts/image_to_usb.sh
+++ b/src/scripts/image_to_usb.sh
@@ -51,6 +51,9 @@ then
   SYSROOT="${FLAGS_build_root}/${FLAGS_board}"
 else
   SYSROOT="${DEFAULT_CHROOT_DIR}${FLAGS_build_root}/${FLAGS_board}"
+  echo "Caching sudo authentication"
+  sudo -v
+  echo "Done"
 fi
 AUTOTEST_SRC="${SYSROOT}/usr/local/autotest"
 
@@ -94,11 +97,6 @@ fi
 FLAGS_from=`eval readlink -f ${FLAGS_from}`
 FLAGS_to=`eval readlink -f ${FLAGS_to}`
 
-# Done evaluating arguments, lets go!
-echo "Caching sudo authentication"
-sudo -v
-echo "Done"
-
 # Use this image as the source image to copy
 SRC_IMAGE="${FLAGS_from}/chromiumos_image.bin"