Improvements to the original sharing implementation.

- Print the mount table as in /proc/self/mountinfo
- Do not exit prematurely when one of the ipc mounts doesn't exist.
- Do not exit prematurely when one of the ipc mounts cannot be unmounted.
- Add a unit test to see if the cleanup really works.
- Use syscall.MNT_DETACH to cleanup mounts after a crash.
- Unmount IPC mounts when the daemon unregisters an old running container.

Signed-off-by: David Calavera <david.calavera@gmail.com>

integration-cli/docker_cli_daemon_test.go

@@ -1474,9 +1474,11 @@ func (s *DockerDaemonSuite) TestCleanupMountsAfterCrash(c *check.C) {
 	id := strings.TrimSpace(out)
 	c.Assert(s.d.cmd.Process.Signal(os.Kill), check.IsNil)
 	c.Assert(s.d.Start(), check.IsNil)
-	mountOut, err := exec.Command("mount").CombinedOutput()
+	mountOut, err := ioutil.ReadFile("/proc/self/mountinfo")
 	c.Assert(err, check.IsNil, check.Commentf("Output: %s", mountOut))
-	c.Assert(strings.Contains(string(mountOut), id), check.Equals, false, check.Commentf("Something mounted from older daemon start: %s", mountOut))
+
+	comment := check.Commentf("%s is still mounted from older daemon start:\nDaemon root repository %s\n%s", id, s.d.folder, mountOut)
+	c.Assert(strings.Contains(string(mountOut), id), check.Equals, false, comment)
 }
 
 func (s *DockerDaemonSuite) TestRunContainerWithBridgeNone(c *check.C) {