aomdec.sh : Make this test create files if needed to test decoder.

If test files don't already exist it calls aomenc to create them.

cherry-picked #ee9ac321 from aom/master

Change-Id: I0e0f33cb60b3492e9106d6c9e2c51f64f71ebb63
diff --git a/test/simple_decoder.sh b/test/simple_decoder.sh
index 27b3a0e..ac3a07b 100755
--- a/test/simple_decoder.sh
+++ b/test/simple_decoder.sh
@@ -45,7 +45,7 @@
   if [ "$(av1_decode_available)" = "yes" ]; then
     if [ ! -e "${AV1_IVF_FILE}" ]; then
       local file="${AOM_TEST_OUTPUT_DIR}/test_encode.ivf"
-      encode_yuv_raw_input_av1 "${file}"
+      encode_yuv_raw_input_av1 "${file}" --ivf
       simple_decoder "${file}" av1 || return 1
     else
       simple_decoder "${AV1_IVF_FILE}" av1 || return 1