Add a Server type that links the FUSE protocol with the virtio
transport. It parses messages sent on the virtio queue and then
calls the appropriate method of the Filesystem trait.
This code has been ported over from crosvm commit
961461350c0b6824e5f20655031bf6c6bf6b7c30.
One small modification has been applied to the original code. Because
cloud-hypervisor didn't have the macro used by crosvm, the match
statement in the function handle_message() has been updated.
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
