caps: check uid and euid
caps: check uid and euid

When we are running inside of a user namespace getuid() will return a
non-zero uid. So let's check euid as well to make sure we correctly drop
capabilities

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@ubuntu.com>

ss1h2a3tw/lxc,hallyn/lxc,hallyn/lxc,ss1h2a3tw/lxc,ss1h2a3tw/lxc,hallyn/lxc