systemd uses SIGRTMIN+n signals, but containerd didn't support the signals
since Go's sys/unix doesn't support them.
This change introduces SIGRTMIN+n handling by utilizing moby/sys/signal.
Fixes#5402.
https://www.freedesktop.org/software/systemd/man/systemd.html#Signals
Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>
Includes 6635b4f0c6,
which fixes a vulnerability in runc that allows a container escape (CVE-2019-5736)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>