Move bash completion logic to new subcommand: save

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

contrib/completion/bash/docker

@@ -2203,7 +2203,21 @@ _docker_image_rmi() {
 }
 
 _docker_image_save() {
-	_docker_save
+	case "$prev" in
+		--output|-o)
+			_filedir
+			return
+			;;
+	esac
+
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--help --output -o" -- "$cur" ) )
+			;;
+		*)
+			__docker_complete_images
+			;;
+	esac
 }
 
 _docker_image_tag() {
@@ -3068,21 +3082,7 @@ _docker_run() {
 }
 
 _docker_save() {
-	case "$prev" in
-		--output|-o)
-			_filedir
-			return
-			;;
-	esac
-
-	case "$cur" in
-		-*)
-			COMPREPLY=( $( compgen -W "--help --output -o" -- "$cur" ) )
-			;;
-		*)
-			__docker_complete_images
-			;;
-	esac
+	_docker_image_save
 }
 
 _docker_search() {