HostsFileReader#getHostDetails is very expensive on large clusters

After upgrading one of our large clusters to 2.8 we noticed many IPC server threads of the resourcemanager spending time in NodesListManager#isValidNode which in turn was calling HostsFileReader#getHostDetails. The latter is creating complete copies of the include and exclude sets for every node heartbeat, and these sets are not small due to the size of the cluster. These copies are causing multiple resizes of the underlying HashSets being filled and creating lots of garbage.