Only increment acquiredSize() once resource has been allocated (#130)
This commit ensures the acquiredSize() metric is only updated when the
resource has been allocated, and is about to be handed off to the
subscriber of acquire().
The decrement in case of allocation error is thus not needed anymore.
Make log quieter in CommonPoolTest#pendingLimitAsync (#131)
The test would log an `ErrorCallbackNotImplemented` but the error is
actually evaluated in a `doOnError`, so we can suppress this output
by subscribing with an empty error handler.