Include named volumes in container migration

When migrating a container with associated volumes, the content of
these volumes should be made available on the destination machine.

This patch enables container checkpoint/restore with named volumes
by including the content of volumes in checkpoint file. On restore,
volumes associated with container are created and their content is
restored.

The --ignore-volumes option is introduced to disable this feature.

Example:

 # podman container checkpoint --export checkpoint.tar.gz <container>

The content of all volumes associated with the container are included
in `checkpoint.tar.gz`

 # podman container checkpoint --export checkpoint.tar.gz --ignore-volumes <container>

The content of volumes is not included in `checkpoint.tar.gz`. This is
useful, for example, when the checkpoint/restore is performed on the
same machine.

 # podman container restore --import checkpoint.tar.gz

The associated volumes will be created and their content will be
restored. Podman will exit with an error if volumes with the same
name already exist on the system or the content of volumes is not
included in checkpoint.tar.gz

 # podman container restore --ignore-volumes --import checkpoint.tar.gz

Volumes associated with container must already exist. Podman will not
create them or restore their content.

Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org>

libpod/container_api.go

@@ -703,6 +703,9 @@ type ContainerCheckpointOptions struct {
 	// important to be able to restore a container multiple
 	// times with '--import --name'.
 	IgnoreStaticMAC bool
+	// IgnoreVolumes tells the API to not export or not to import
+	// the content of volumes associated with the container
+	IgnoreVolumes bool
 }
 
 // Checkpoint checkpoints a container