Fix bug in HTTP/2 outbound flow control

Motivation:

The outbound flow controller logic does not properly reset the allocated
bytes between successive invocations of the priority algorithm.

Modifications:

Updated the priority algorithm to reset the allocated bytes for each
stream.

Result:

Each call to the priority algorithm now starts with zero allocated bytes
for each stream.
It is fine to leave it but if you size it for the amount of objects you are expecting you get the following benefits:

1) Array does not have room for "client" and "server" streams and so indexing can be designed to catch results for unexpected streamIds.  So test could throw exception if index is for example not odd, or at the very least overwrite a value and cause a failure in value verification.
2) Array isn't double the required size
3) Array indexing at verification doesn't have to go "+=2" and can use the more traditional single increment approach.

I agree it is unit test code but for a shared piece of software like netty test code can often be referenced for production code (not that we can control how people copy/paste our code but we can help by removing bad temptations).