Added the options for client credential and refresh token + fixed unit test  for MongoDb

I added the options for client credential and refresh token grant types. In particular, the refresh token option `always_issue_new_refresh_token` set to true generate a new refresh_token on each refresh call.
I added the `options` key in the `zf-oauth2` configuration, to be able to pass all the [parameters of the OAuth2\Server](https://github.com/bshaffer/oauth2-server-php/blob/develop/src/OAuth2/Server.php#L115-L128) class.
I also fixed the unit test for the MongoDb adapter, now if MongoDb is not running it does not report errors.