Drop capabilities in dockerinit instead of with lxc utils, since
libvirt-lxc doesn't support it.
This will also be needed for machine container mode, since dockerinit
needs CAP_SYS_ADMIN to setup /dev/console correctly.
Upstream-commit: b8f1c7370516a4eec0d3168d594a7d7d92e7f8e9
Component: engine