hostfs bootparametres file

Hi all,

I would like to report a potential bug and a possible correction to the boot_parameters hostfs file corruption.

What's the bug, how can we reproduce it?
========================================
* Start marionnet (id will begin at 1)
* create a project and 2 machines (indeed i have tested with 3 machines, but 2 should be enough) m1 and m2 (m1 will have internal id 1 ) (m2 will have internal id 2)
* add interface information on m1 only through GUI, so that boot_parameters file will be big enough for m1, dont modify m2 configuration.
* start machines (this will create hostfs and subdir 1 and 2 )
* stop machines
* save project (this will save hostfs subdirectories: m2 as 2, m1 as 1)
* close marionnet, and start it again (so that id starts again at 1)
* load project
(this will restore hostfs and subdirectories 1 and 2)
* start project
(this will start m2 as internal id 1, and m1 as internal id 2)
Unfortunately it does not *erase* the file, just overwrite it (the beginning), the end remains which corrupt file... (name and other parameters...)

Proposal to Fix Issue:
======================
Go to simulation_level.ml line 1162 and change to the following:
Unix.openfile boot_parameters_pathname [Unix.O_WRONLY; Unix.O_CREAT ; Unix.O_TRUNC] 0o777

Best regards.