Retry on failure

This works around the fact that the VM does not preserve errno/GetLastError across API calls.

Author: brianquinlan

pkgs/io_file/dart_test.yaml

@@ -1,3 +1,10 @@
 concurrency: 1
 reporter: compact
 test-randomize-ordering-seed: random
+tags:
+  # TODO(brianquinlan): Remove retries when
+  # https://github.com/dart-lang/sdk/issues/38832 is fixed.
+  android || ios || linux || mac-os:
+    retry: 2
+  windows:
+    retry: 5