Fixes in #426

https://github.com/FriendsOfSymfony/FOSElasticaBundle/pull/426 is currently causing a few headaches:

1) Using both `no stop on error` and `stop on error` simultaneously is confusing. I for now used `stop on error` but I'd be happy to change it.
2) Fixed `AbstractProviderTest::testPopulateNotStopOnError`
3) IMO the "stop on error" option should be a boolean only. Therefore I changed `empty($options['no-stop-on-error'])` into `is_bool($options['stop-on-error'])`.