[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.
Are we sure we want to automatically purge the target directory here? Maybe we should say that the target directory has to be empty and fail if it is not.