Add bash completion for swarm ca

Signed-off-by: Harald Albers <github@albersweb.de>
(cherry picked from commit 5bd00a563e)
Signed-off-by: Andrew Hsu <andrewhsu@docker.com>

components/cli/contrib/completion/bash/docker

@@ -3292,6 +3292,7 @@ _docker_service_update_and_create() {
 
 _docker_swarm() {
 	local subcommands="
+		ca
 		init
 		join
 		join-token
@@ -3312,6 +3313,24 @@ _docker_swarm() {
 	esac
 }
 
+_docker_swarm_ca() {
+	case "$prev" in
+		--ca-cert|--ca-key)
+			_filedir
+			return
+			;;
+		--cert-expiry|--external-ca)
+			return
+			;;
+	esac
+
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--ca-cert --ca-key --cert-expiry --detach -d --external-ca --help --quiet -q --rotate" -- "$cur" ) )
+			;;
+	esac
+}
+
 _docker_swarm_init() {
 	case "$prev" in
 		--advertise-addr)