This create a directory by node to allow feature like save as
to work when running on multiple compute. Benefits now dynamips work
like other nodes. Old topologies are migrated.
Ref https://github.com/GNS3/gns3-gui/issues/1761
This monitor for change the file from dynamips by computing a
hash of the watched file.
The way dynamips work prevent the update of the modification time.
We can improve that by using native system for watching file but:
* it's require dependencies specific for each OS
* dependencies use C extensions
* this is only a backup if your router is cleanly shutdown we export
stuff
