Add Load method to factory

Also update Initialize to take a path to the container
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)

factory.go

@@ -1,17 +1,25 @@
 package libcontainer
 
 type Factory interface {
-	// Initializes a new container with the specified ID and config. The ID is a user-provided
-	// opaque identifier. Starts an init process with the initialProcess config inside the new
-	// container.
+	// Initializes a new container in the given path. A unique ID is generated for the container and
+	// starts the initial process inside the container.
 	//
-	// Returns the new container and the PID of the new init inside the container.
-	// The caller must reap this PID.
+	// Returns the new container with a running process.
 	//
-	// Errors: ID already exists,
-	//         config or initialConfig is invalid,
-	//         system error.
+	// Errors:
+	// Path already exists
+	// Config or initialConfig is invalid
+	// System error
 	//
 	// On error, any partially created container parts are cleaned up (the operation is atomic).
-	Initialize(id string, config *Config, initialProcess *ProcessConfig) (*Container, int, error)
+	Initialize(path string, config *Config) (Container, error)
+
+	// Load takes the path for an existing container and reconstructs the container
+	// from the state.
+	//
+	// Errors:
+	// Path does not exist
+	// Container is stopped
+	// System error
+	Load(path string) (Container, error)
 }