Fixed PHP-773: Fix the persistence issue with logging stream contexts

Each time we instanciate MongoClient we will iterate over open servers
and apply the current stream contexts.
This will overwrite previously set contexts with the new one or reset it
to NULL if no context was provided.

If there are no open streams, we assign the context to the server
options and it will be used when creating new streams like before
Update test, we print this message out one more time when creating

multiple MongoClients since we have to find the server stream to
overwrite the stream context
server_def -> server_definition and remove a WS as per CR
Merge pull request #518 from bjori/PHP-773-context-persistance

Fixed PHP-773: Fix the persistence issue with logging stream contexts

* bjori/PHP-773-context-persistance:
  server_def -> server_definition and remove a WS as per CR
  Update test, we print this message out one more time when creating
  Fixed PHP-773: Fix the persistence issue with logging stream contexts