Backport a fix from upstream to make volumes rprivate by default

[rhvgoyal]

We need to backport following fix from upstream to make volumes "rprivate" by default.

moby#32851

[rhvgoyal]

cc @runcom

[runcom]

@rhvgoyal which branches are going to need this? was #238 meant to address this and this issue is just a placeholder for 1.13.1 and 17.03.1-ce branches? (I didn't fully understood). Meanwhile, I've opened two PRs to port #238 to 1.13.1 and 17.03.1-ce, but again, I'm unsure if we still need moby#32851 in every branch as well, please let me know.

[rhvgoyal]

@runcom

#238 and this PR are two independent fixes. Though problem description remains the same.

This PR is basically fixing a regression introduced by commit

moby@fc7b904

I had noticed that above commit did not make into 1.12.6. So we will need this fix for 1.13.1 and
any branches after that.

[runcom]

Backported moby@af8a143 to docker-1.13.1, docker-1.13.1-rhel, docker-17.03.1-ce