vmm: properly set vcpu state when thread exited

Once error occur, vcpu thread may exit, this should
be critical event for the whole VM, we should fire
exit event and set vcpu state.

If we don't set vcpu state, the shutdown process
will hang at signal_thread, which is waiting the
vcpu state to change.

Signed-off-by: Yong He <alexyonghe@tencent.com>

vmm/src/cpu.rs

@@ -1011,12 +1011,16 @@ impl CpuManager {
                                             "VCPU generated error: {:?}",
                                             Error::UnexpectedVmExit
                                         );
+                                        vcpu_run_interrupted.store(true, Ordering::SeqCst);
+                                        exit_evt.write(1).unwrap();
                                         break;
                                     }
                                 },
 
                                 Err(e) => {
                                     error!("VCPU generated error: {:?}", Error::VcpuRun(e.into()));
+                                    vcpu_run_interrupted.store(true, Ordering::SeqCst);
+                                    exit_evt.write(1).unwrap();
                                     break;
                                 }
                             }