Description of problem:
With the most updated RHEL and Atomic, running an image with --read-only fails and returns an error.

Version-Release number of selected component (if applicable):

# atomic host status
  TIMESTAMP (UTC)         VERSION     ID             OSNAME               REFSPEC                                                        
* 2016-03-01 01:35:21     7.2.2-2     8b2cf24b42     rhel-atomic-host     rhel-atomic-host-ostree:rhel-atomic-host/7/x86_64/standard     

# docker version
Client:
 Version:      1.8.2-el7
 API version:  1.20
 Package Version: docker-1.8.2-10.el7.x86_64
 Go version:   go1.4.2
 Git commit:   a01dc02/1.8.2

How reproducible:
Trivial

Steps to Reproduce:
1. # docker run --read-only --name sleeper registry.access.redhat.com/rhel7/rhel:latest sleep 1m

Actual results:
Timestamp: 2016-03-10 16:42:44.672730324 +0000 UTC
Code: System error

Message: read-only file system

Frames:
---
0: setupRootfs
Package: github.com/opencontainers/runc/libcontainer
File: rootfs_linux.go@39
---
1: Init
Package: github.com/opencontainers/runc/libcontainer.(*linuxStandardInit)
File: standard_init_linux.go@52
---
2: StartInitialization
Package: github.com/opencontainers/runc/libcontainer.(*LinuxFactory)
File: factory_linux.go@242
---
3: initializer
Package: github.com/docker/docker/daemon/execdriver/native
File: init.go@35
---
4: Init
Package: github.com/docker/docker/pkg/reexec
File: reexec.go@26
---
5: main
Package: main
File: docker.go@19
---
6: main
Package: runtime
File: proc.go@63
---
7: goexit
Package: runtime
File: asm_amd64.s@2232
Error response from daemon: Cannot start container 3e3fdabf598d6a590d690a94947fe4c6adc15ec17c84f70bc1415eb3e98bf98e: [8] System error: read-only file system


Expected results:
Container should start, sleep, then exit gracefully after one minute