[BZ 1074636] Add ability to move storage node datafiles

This patch would add the ability of moving commit_log, saved_caches and a single data directories to a new location. The process is time consuming and involves shutting down the storage node before doing the move and configuration update. If it's a single node deployment, this will turn the server to maintenance mode while doing the move. It also means that this patch will not able to restart the node, as agent will stop accepting the command (there's a separate discussion of that in rhq-devel, and solving that issue is required before this can be merged).

This change also provides the storage node with one new operation, "moveDataFiles" and changes the behaviour of updateConfiguration operation.
I was wondering about this issue, and also thought about the possibility of only allowing user to customize the values - but not do any actual file moving (in case user wants to do that manually). The method was there, so I just extended it, but I would agree that removing the whole operation (pluginConfiguration) would make sense, since all this is available from storage node administration anyway.