test: retry on known SmartOS bug

There is a known issue with SmartOS that is generally worked around
in `tools/test.py`. However, a more robust workaround is required for
some tests that open many network connections.

`test-http-regr-gh-2928` is one such test.

Fixes: https://github.com/nodejs/node/issues/5445
Refs: https://github.com/nodejs/node/pull/3941
PR-URL: https://github.com/nodejs/node/pull/5454


Reviewed-By: Fedor Indutny <fedor@indutny.com>