test: mark test-repl-persistent-history as flaky

This test is already being investigated, but until a solution is found
it should be marked flaky.

Ref: https://github.com/nodejs/node/issues/2319
Ref: https://github.com/nodejs/node/pull/2356

PR-URL: https://github.com/nodejs/node/pull/2659


Reviewed-By: orangemocha - Alexis Campailla <orangemocha@nodejs.org>