histogram_rt_SUITE: minor improvements

git-svn-id: https://scalaris.googlecode.com/svn/trunk@6651 71766da9-9752-0410-ab17-bfafa751c56a
dht_node_move, jump: improve passing known nodes (ref. r6110)

- remove duplicate nodes (in small rings, nodes may be in the pred and succ list
- no need to get a node_details structure - get the neighborhood structure instead

git-svn-id: https://scalaris.googlecode.com/svn/trunk@6652 71766da9-9752-0410-ab17-bfafa751c56a
wip