vmm: (Re-)Introduce a VMM structure

Unlike the Vmm structure we removed with commit bdfd1a3f, this new one
is really meant to represent the VM monitoring/management object.
For that, we implement a control loop that will replace the one that's
currently embedded within the Vm structure itself.
This will allow us to decouple the VM lifecycle management from the VM
object itself, by having a constantly running VMM control loop.

Besides the VM specific events (exit, reset, stdin for now), the VMM
control loop also handles all the Cloud Hypervisor IPC requests.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

src/main.rs

@@ -286,7 +286,7 @@ fn main() {
     );
 
     if let Err(e) = vmm::start_vm_loop(Arc::new(vm_config)) {
-        println!("Guest boot failed: {}", e);
+        println!("Guest boot failed: {:?}", e);
         process::exit(1);
     }
 }