Add context and client to SpecOpts

In order to do more advanced spec generation with images, snapshots,
etc, we need to inject the context and client into the spec generation
code.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

spec.go

@@ -1,16 +1,20 @@
 package containerd
 
-import specs "github.com/opencontainers/runtime-spec/specs-go"
+import (
+	"context"
+
+	specs "github.com/opencontainers/runtime-spec/specs-go"
+)
 
 // GenerateSpec will generate a default spec from the provided image
 // for use as a containerd container
-func GenerateSpec(opts ...SpecOpts) (*specs.Spec, error) {
+func GenerateSpec(ctx context.Context, client *Client, opts ...SpecOpts) (*specs.Spec, error) {
 	s, err := createDefaultSpec()
 	if err != nil {
 		return nil, err
 	}
 	for _, o := range opts {
-		if err := o(s); err != nil {
+		if err := o(ctx, client, s); err != nil {
 			return nil, err
 		}
 	}