Move client's options to separate files

This should help in discovering the available options for a given object.

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

task_opts.go

@@ -0,0 +1,27 @@
+package containerd
+
+import (
+	"context"
+
+	"github.com/containerd/containerd/linux/runcopts"
+	"github.com/containerd/containerd/mount"
+)
+
+// NewTaskOpts allows the caller to set options on a new task
+type NewTaskOpts func(context.Context, *Client, *TaskInfo) error
+
+// WithRootFS allows a task to be created without a snapshot being allocated to its container
+func WithRootFS(mounts []mount.Mount) NewTaskOpts {
+	return func(ctx context.Context, c *Client, ti *TaskInfo) error {
+		ti.RootFS = mounts
+		return nil
+	}
+}
+
+// WithExit causes the task to exit after a successful checkpoint
+func WithExit(r *CheckpointTaskInfo) error {
+	r.Options = &runcopts.CheckpointOptions{
+		Exit: true,
+	}
+	return nil
+}