Add initial containerd *Client

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

spec.go

@@ -0,0 +1,44 @@
+package containerd
+
+import specs "github.com/opencontainers/runtime-spec/specs-go"
+
+type SpecOpts func(s *specs.Spec) error
+
+func WithImageRef(ref string) SpecOpts {
+	return func(s *specs.Spec) error {
+		if s.Annotations == nil {
+			s.Annotations = make(map[string]string)
+		}
+		s.Annotations["image"] = ref
+		return nil
+	}
+}
+
+func WithHostname(id string) SpecOpts {
+	return func(s *specs.Spec) error {
+		s.Hostname = id
+		return nil
+	}
+}
+
+func WithArgs(args ...string) SpecOpts {
+	return func(s *specs.Spec) error {
+		s.Process.Args = args
+		return nil
+	}
+}
+
+// GenerateSpec will generate a default spec from the provided image
+// for use as a containerd container
+func GenerateSpec(opts ...SpecOpts) (*specs.Spec, error) {
+	s, err := createDefaultSpec()
+	if err != nil {
+		return nil, err
+	}
+	for _, o := range opts {
+		if err := o(s); err != nil {
+			return nil, err
+		}
+	}
+	return s, nil
+}