This commit changes the way that consensus.Clean() works. Before
it deleted the whole data folder. Now it renames it as <name>.old.0
and leaves it. When Clean() is called again, it renames <name>.old.0
as <name>.old.1, and the actual data becomes <name>.old.0. Higher number
means older. The number of backups is fixed to 5. When 5 backups exists
and a new one comes up again, the last one is discarded.
License: MIT
Signed-off-by: Hector Sanjuan <hector@protocol.ai>
