Move shim client into subpackage

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

linux/shim/client/client_linux.go

@@ -0,0 +1,34 @@
+// +build linux
+
+package client
+
+import (
+	"os/exec"
+	"syscall"
+
+	"github.com/containerd/cgroups"
+	"github.com/pkg/errors"
+)
+
+func getSysProcAttr(nonewns bool) *syscall.SysProcAttr {
+	attr := syscall.SysProcAttr{
+		Setpgid: true,
+	}
+	if !nonewns {
+		attr.Cloneflags = syscall.CLONE_NEWNS
+	}
+	return &attr
+}
+
+func setCgroup(cgroupPath string, cmd *exec.Cmd) error {
+	cg, err := cgroups.Load(cgroups.V1, cgroups.StaticPath(cgroupPath))
+	if err != nil {
+		return errors.Wrapf(err, "failed to load cgroup %s", cgroupPath)
+	}
+	if err := cg.Add(cgroups.Process{
+		Pid: cmd.Process.Pid,
+	}); err != nil {
+		return errors.Wrapf(err, "failed to join cgroup %s", cgroupPath)
+	}
+	return nil
+}