[Forknet] Lock vital files to prevent mocknet corruption

[VanBarbascu]

Forknet has files like that should be immutable. Suck files are snapshots used to revert to when a test is restarted. Getting in that state takes time to achieve and if one host gets corrupted, it may invalidate the whole forknet test.

To prevent accidental loss, those files can be marked as immutable with file attributes:

# set the immutable attribute
sudo chattr +i folder_name

# remove the immutable attribute
sudo chattr -i folder_name