As per the current implementation for AM blacklisting, disabling is based on complete cluster resource.
Incase of partitioned cluster though, nodes applicable for AM labels only should be considered as total nodes.
Additionally for unmanaged AM as AM blacklisting is not done as AM is not launched by RM, it is equivalent to AM blacklisting being disabled for this app. Hence we do not need to create a SimpleBlacklistManager object in RMAppImpl#createNewAttempt.
We can create DisabledBlacklistManager object instead.