Move bash completion logic to new subcommand: tag

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

contrib/completion/bash/docker

@@ -2221,7 +2221,25 @@ _docker_image_save() {
 }
 
 _docker_image_tag() {
-	_docker_tag
+	case "$cur" in
+		-*)
+			COMPREPLY=( $( compgen -W "--help" -- "$cur" ) )
+			;;
+		*)
+			local counter=$(__docker_pos_first_nonflag)
+
+			if [ $cword -eq $counter ]; then
+				__docker_complete_image_repos_and_tags
+				return
+			fi
+			(( counter++ ))
+
+			if [ $cword -eq $counter ]; then
+				__docker_complete_image_repos_and_tags
+				return
+			fi
+			;;
+	esac
 }
 
 
@@ -3129,25 +3147,7 @@ _docker_stop() {
 }
 
 _docker_tag() {
-	case "$cur" in
-		-*)
-			COMPREPLY=( $( compgen -W "--help" -- "$cur" ) )
-			;;
-		*)
-			local counter=$(__docker_pos_first_nonflag)
-
-			if [ $cword -eq $counter ]; then
-				__docker_complete_image_repos_and_tags
-				return
-			fi
-			(( counter++ ))
-
-			if [ $cword -eq $counter ]; then
-				__docker_complete_image_repos_and_tags
-				return
-			fi
-			;;
-	esac
+	_docker_image_tag
 }
 
 _docker_unpause() {