runc only works on Linux so remove putative Solaris and unsupported main

Solaris runc equivalent is not open source. The unsupported option does
not build as other code is Linux specific.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

init.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"os"
+	"runtime"
+
+	"github.com/opencontainers/runc/libcontainer"
+	_ "github.com/opencontainers/runc/libcontainer/nsenter"
+	"github.com/urfave/cli"
+)
+
+func init() {
+	if len(os.Args) > 1 && os.Args[1] == "init" {
+		runtime.GOMAXPROCS(1)
+		runtime.LockOSThread()
+	}
+}
+
+var initCommand = cli.Command{
+	Name:  "init",
+	Usage: `initialize the namespaces and launch the process (do not call it outside of runc)`,
+	Action: func(context *cli.Context) error {
+		factory, _ := libcontainer.New("")
+		if err := factory.StartInitialization(); err != nil {
+			// as the error is sent back to the parent there is no need to log
+			// or write it to stderr because the parent process will handle this
+			os.Exit(1)
+		}
+		panic("libcontainer: container init failed to exec")
+	},
+}