virtcontainers: Initial import

This is a virtcontainers 1.0.8 import into Kata Containers runtime.

virtcontainers is a Go library designed to manage hardware virtualized
pods and containers. It is the core Clear Containers framework and will
become the core Kata Containers framework, as discussed at
https://github.com/kata-containers/runtime/issues/33

Some more more pointers:

virtcontainers README, including some design and architecure notes:
https://github.com/containers/virtcontainers/blob/master/README.md

virtcontainers 1.0 API:
https://github.com/containers/virtcontainers/blob/master/documentation/api/1.0/api.md

Fixes #40

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

virtcontainers/spawner.go

@@ -0,0 +1,65 @@
+//
+// Copyright (c) 2016 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+package virtcontainers
+
+import (
+	"fmt"
+)
+
+// SpawnerType describes the type of guest agent a Pod should run.
+type SpawnerType string
+
+const (
+	// NsEnter is the nsenter spawner type
+	NsEnter SpawnerType = "nsenter"
+)
+
+// Set sets an agent type based on the input string.
+func (spawnerType *SpawnerType) Set(value string) error {
+	switch value {
+	case "nsenter":
+		*spawnerType = NsEnter
+		return nil
+	default:
+		return fmt.Errorf("Unknown spawner type %s", value)
+	}
+}
+
+// String converts an agent type to a string.
+func (spawnerType *SpawnerType) String() string {
+	switch *spawnerType {
+	case NsEnter:
+		return string(NsEnter)
+	default:
+		return ""
+	}
+}
+
+// newSpawner returns an agent from and agent type.
+func newSpawner(spawnerType SpawnerType) spawner {
+	switch spawnerType {
+	case NsEnter:
+		return &nsenter{}
+	default:
+		return nil
+	}
+}
+
+// spawner is the virtcontainers spawner interface.
+type spawner interface {
+	formatArgs(args []string) ([]string, error)
+}