Setup builtin host plugin with capabilities

builtin/myplugin/host/cap/write_hello.go

@@ -0,0 +1,8 @@
+package cap
+
+import "io/ioutil"
+
+func WriteHello() {
+	data := []byte("hello\ngo\n")
+	ioutil.WriteFile("/tmp/dat1", data, 0644)
+}

builtin/myplugin/host/osx.go

@@ -0,0 +1,36 @@
+package host
+
+import (
+	"github.com/hashicorp/vagrant-plugin-sdk/component"
+	sdkcore "github.com/hashicorp/vagrant-plugin-sdk/core"
+	"github.com/hashicorp/vagrant/builtin/myplugin/host/cap"
+)
+
+type HostConfig struct {
+}
+
+// TestOSXHost is a Host implementation for myplugin.
+type OSXHost struct {
+	config HostConfig
+
+	// Include capability host
+	sdkcore.CapabilityHost
+}
+
+// DetectFunc implements component.Host
+func (h *OSXHost) DetectFunc() interface{} {
+	return h.Detect()
+}
+
+func (h *OSXHost) Detect() bool {
+	return true
+}
+
+func (h *OSXHost) InitializeCapabilities() {
+	h.RegisterCapability("write_hello", cap.WriteHello)
+}
+
+var (
+	_ component.Host = (*OSXHost)(nil)
+	_ sdkcore.Host   = (*OSXHost)(nil)
+)