Refactor mounts into pkg to make changes easier

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/mount/readonly.go

@@ -0,0 +1,12 @@
+// +build linux
+
+package mount
+
+import (
+	"github.com/dotcloud/docker/pkg/system"
+	"syscall"
+)
+
+func SetReadonly() error {
+	return system.Mount("/", "/", "bind", syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_REC, "")
+}