overlay: do not check for idmapped mounts if euid!=0
overlay: do not check for idmapped mounts if euid!=0

do not store the result of the check when running with euid != 0.  The
check must happen and its result stored only once the process is
re-executed in its user namespace and runs with euid == 0.

It doesn't make any real difference at the moment since the  kernel
feature is going to be supported only for root in the initial user
namespace.

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

containers/storage,containers/storage,containers/storage