Fix MongoError: No more documents in tailed cursor

[jaydp17]

The issue has been described on mosca/issues/346.

For more info : MongoError: No more documents in tailed cursor

Found the solution from the below StackOverflow question
Finding each new document in mongoDB oplog collection using nodejs does not work (cursor seems to become invalid or dead)

[jaydp17]

I don't know why the tests fail, but messages are delivered. I'd recommend you too verify that.
I tried to figure out the reason for tests failing but didn't quite get it.
You see any clue ?

[mcollina]

I don't see:

1. why this solves the problem in [MongoDb] No more documents in tailed cursor mosca#346
2. it seems to me that error you are seeing is 'Stats failed: MongoError: unauthorized', because that is what it is failing the re-initialization of the cursor
3. the attached code can't work, because handle() returns a function: https://github.com/mcollina/ascoltatori/blob/master/lib/mongo_ascoltatore.js#L139-L160, you probably forgot some more change

@cfan8 I think this is related to #132.

[jaydp17]

1. I don't know why it solves, but I read about it in this StackOverflow question. Also, Cursor.each is deprecated.
2. I don't get Stats failed: MongoError: unauthorized after this patch.
3. Yes, I know handle() returns a function, and I call it here

Also, I went back before #131 was merged and tried it. I do get Stats failed: MongoError: unauthorized

[mcollina]

Can you complete the refactor to remove the deprecation of Cursor.each. The handle function does not need to return a function at all, we can just call it through.

Moreover, all unit tests related to MongoDB fails, so there is some more problem in here.

Keep up the good work anyway, sorry that I've missed that call!

[jaydp17]

It might take me some time to get back to this, but i'll finish it for sure

[mcollina]

Is the problem described still valid? Things are working fine with 2.0.0 now. Please check and in case reopen this PR basing it on top of v2.