TableHistograms output a lot of repeated information

This patch aims to fix two issues:

1. the original output of nodetool tablehistograms with no tables specified is wrong , the output will contains many repeated informations. See the picture below.

The reason is that for tablesList.keys() will give a Multiset output as tablesList is a Multimap.

2. as we have DISCUSS for "Change the useage of nodetool tablehistograms" , for arguments more than two, the output of tablehistograms will be all of the tables, it's a bug that we should fix. We can see that the description of tablehistograms is ,out put the statistic histograms for the given table. and the format of the argument is like tthis