docker_exec: SIGKILL/SIGSTOP can not be trapped
docker_exec: SIGKILL/SIGSTOP can not be trapped

As per SC2173, SIGKILL and SIGSTOP can not be caught/ignored (according to POSIX and as implemented on platforms including Linux and FreeBSD).
Trying to trap this signal has undefined results.
So removing this call.

Signed-off-by: Sébastien Han <62d754cc350e84d3b1c32ae79f976f5348e74a40@redhat.com>

ceph/ceph-docker,ceph/ceph-docker