number_of_chunks from client are respected by the server while finalizing upload of chunks

[labheshd]

Is your feature request related to a problem? Please describe.
Currently, after #310, the server will no longer respect the number_of_chunks sent up by the client during upload operation.
This can cause an issue, as the open saves backend can't figure out if the upload that the client performed was complete or not.
Ex: If the client was supposed to send 10 chunks, without the client explicitly telling the open saves backend how many chunks will be uploaded beforehand, the open saves backend can't understand if the upload was completed or not.

Describe the solution you'd like
number_of_chunks sent by the client at the start of the upload operation should be respected and a check should be made on the backend while finalizing the upload operation, to ensure all the chunks that were supposed to be uploaded were in fact uploaded. If the number of chunks dont match the number_of_chunks value, an error is returned to the client, indicating that the upload isn't complete.

[ghost]

In our gateway, we want to solve this by passing an "ExpectedNumberOfChunks" to the gateway when initializing the upload. This value will be checked against the numberOfChunks when the issue #315 will be resolved.