Move bash completion logic to new subcommand: rmi

Signed-off-by: Harald Albers <github@albersweb.de>

contrib/completion/bash/docker

@@ -2188,7 +2188,14 @@ _docker_image_remove() {
 }
 
 _docker_image_rm() {
-	_docker_rmi
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--force -f --help --no-prune" -- "$cur" ) )
+			;;
+		*)
+			__docker_complete_images
+			;;
+	esac
 }
 
 _docker_image_rmi() {
@@ -3053,14 +3060,7 @@ _docker_rm() {
 }
 
 _docker_rmi() {
-	case "$cur" in
-		-*)
-			COMPREPLY=( $( compgen -W "--force -f --help --no-prune" -- "$cur" ) )
-			;;
-		*)
-			__docker_complete_images
-			;;
-	esac
+	_docker_image_rm
 }
 
 _docker_run() {