Add --download-data-only option to run-test.py

tools/run-tests.py

Index: tools/run-tests.py
diff --git a/tools/run-tests.py b/tools/run-tests.py
index 9288bbf14ef88a95812b7aaecb794ba2b3f643b1..3186b0b2fc08b13595681f6003a2bff6bd2ef0d8 100755
--- a/tools/run-tests.py
+++ b/tools/run-tests.py
@@ -206,6 +206,9 @@ def BuildOptions():
                     default="")
   result.add_option("--download-data", help="Download missing test suite data",
                     default=False, action="store_true")
+  result.add_option("--download-data-only",
+                    help="Download missing test suite data and exit",
+                    default=False, action="store_true")
   result.add_option("--extra-flags",
                     help="Additional flags to pass to each test command",
                     default="")
@@ -485,10 +488,13 @@ def Main():
     if suite:
       suites.append(suite)
 
-  if options.download_data:
+  if options.download_data or options.download_data_only:
     for s in suites:
       s.DownloadData()
 
+  if options.download_data_only:
+    return exit_code
+
   for (arch, mode) in options.arch_and_mode:
     try:
       code = Execute(arch, mode, args, options, suites, workspace)