Allow node to serve traffic only once compactions settle

Today when nodes are joined to the cluster, once data streaming is completed, node starts serving traffic, but it's possible there are a lot of pending compactions, so having reads accessing sstables during that time is going to make these reads slower and load the server. In some cases performance is so bad it can bring the application down. 

Today I overcome this by stopping native transport to a node after join finishes, and enabling it after compactions pending reach a certain threshold, it would be nice to have that as part of the join process, only consider join completed once there are not that many compactions pending.