vm-migration: Define the Snapshottable and Transportable traits

A Snapshottable component can snapshot itself and
provide a MigrationSnapshot payload as a result.

A MigrationSnapshot payload is a map of component IDs to a list of
migration sections (MigrationSection). As component can be made of
several Migratable sub-components (e.g. the DeviceManager and its
device objects), a migration snapshot can be made of multiple snapshot
itself.
A snapshot is a list of migration sections, each section being a
component state snapshot. Having multiple sections allows for easier and
backward compatible migration payload extensions.

Once created, a migratable component snapshot may be transported and this
is what the Transportable trait defines, through 2 methods: send and recv.

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

vm-migration/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "vm-migration"
+version = "0.1.0"
+authors = ["The Cloud Hypervisor Authors"]
+edition = "2018"
+
+[dependencies]
+anyhow = "1.0"
+thiserror = "1.0"
+serde = {version = ">=1.0.27", features = ["rc"] }
+serde_derive = ">=1.0.27"
+serde_json = ">=1.0.9"