daemon.Diff already implements mounting for naivegraphdriver and
aufs which does diffing on its owns does not need the container to be mounted.
So new filesystem driver should mount filesystems on their own if it is needed
to implement Diff(). This issue was reported by @kvasdopil while working on a
freebsd port, because freebsd does not allow mount an already mounted
filesystem. Also it saves some cycles for other operating systems as well.
Signed-off-by: Jörg Thalheim <joerg@higgsboson.tk>
Upstream-commit: 6473b0f127c63e8a45b2b456d69e3de03273705c
Component: engine
097c5661ee