Sending capability ids instead of capability names ot LXC for --cap-add and --cap-drop. Also fixed tests. Docker-DCO-1.1-Signed-off-by: Abin Shahab <ashahab@altiscale.com> (github: ashahab-altiscale) Upstream-commit: bff3509e431ce6d68e2accbb842c99d4abe86e05 Component: engine