Add user namespace support to client

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

apparmor.go

@@ -0,0 +1,13 @@
+// +build linux
+
+package containerd
+
+import specs "github.com/opencontainers/runtime-spec/specs-go"
+
+// WithApparmor sets the provided apparmor profile to the spec
+func WithApparmorProfile(profile string) SpecOpts {
+	return func(s *specs.Spec) error {
+		s.Process.ApparmorProfile = profile
+		return nil
+	}
+}