vmm: cpu: Implement the Snapshottable trait

Implement the Snapshottable trait for Vcpu, and then implements it for
CpuManager. Note that CpuManager goes through the Snapshottable
implementation of Vcpu for every vCPU in order to implement the
Snapshottable trait for itself.

Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vmm/src/lib.rs

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 
+extern crate anyhow;
 extern crate arc_swap;
 #[macro_use]
 extern crate lazy_static;