mountinfo.Mounted: return true for /
mountinfo.Mounted: return true for /

Let's assume that the root directory is always mounted
(I can't imagine a case when it's not).

This should speed up Mounted("/") case.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

moby/sys