Modify container exec and attach, add image import/export

Signed-off-by: Matthew Heon <mheon@redhat.com>

libpod/ctr/container.go

@@ -35,17 +35,15 @@ func (c *Container) Kill(signal uint) error {
 }
 
 // Exec starts a new process inside the container
-// TODO does this need arguments?
+// Returns fully qualified URL of streaming server for executed process
-// TODO should this return anything besides error?
+func (c *Container) Exec(cmd []string, tty bool, stdin bool) (string, error) {
-func (c *Container) Exec() error {
+	return "", ErrNotImplemented
-	return ErrNotImplemented
 }
 
 // Attach attaches to a container
-// TODO does this need arguments?
+// Returns fully qualified URL of streaming server for the container
-// TODO should this return anything besides error?
+func (c *Container) Attach(stdin, tty bool) (string, error) {
-func (c *Container) Attach() error {
+	return "", ErrNotImplemented
-	return ErrNotImplemented
 }
 
 // Mount mounts a container's filesystem on the host

libpod/runtime.go

@@ -156,6 +156,16 @@ func (r *Runtime) GetImages(filter ...ImageFilter) ([]*storage.Image, error) {
 	return nil, ctr.ErrNotImplemented
 }
 
+// ImportImage imports an OCI format image archive into storage as an image
+func (r *Runtime) ImportImage(path string) (*storage.Image, error) {
+	return nil, ctr.ErrNotImplemented
+}
+
+// ExportImage exports an image to an OCI archive, saving it at the given path
+func (r *Runtime) ExportImage(image *storage.Image, path string) error {
+	return ctr.ErrNotImplemented
+}
+
 // CommitContainer commits the changes between a container and its image,
 // creating a new image
 // If the container was not created from an image (for example,