cmake: Download testdata over HTTP.

Use HTTP instead of HTTPS to avoid requiring CMake builds with
HTTPS support.

BUG=aomedia:1253

Change-Id: I1c130496ae3ec9ea43629117e3f3f46048a32b92

test/test_data_download_worker.cmake

@@ -18,7 +18,7 @@ if (NOT AOM_ROOT OR NOT AOM_CONFIG_DIR OR NOT AOM_TEST_FILE
 endif ()
 
 set(AOM_TEST_DATA_URL
-    "https://storage.googleapis.com/downloads.webmproject.org/test_data/libvpx")
+    "http://storage.googleapis.com/downloads.webmproject.org/test_data/libvpx")
 
 if (NOT AOM_TEST_DATA_PATH)
   set(AOM_TEST_DATA_PATH "$ENV{LIBAOM_TEST_DATA_PATH}")