ctr: alphabetize commands, rename signals

Signed-off-by: Jess Valarezo <valarezo.jessica@gmail.com>

cmd/ctr/commands/snapshot/snapshot.go

@@ -23,17 +23,17 @@ var Command = cli.Command{
 	Usage: "manage snapshots",
 	Flags: commands.SnapshotterFlags,
 	Subcommands: cli.Commands{
-		listCommand,
-		usageCommand,
-		removeCommand,
-		prepareCommand,
-		viewCommand,
-		treeCommand,
-		mountCommand,
 		commitCommand,
 		infoCommand,
+		listCommand,
+		mountCommand,
+		prepareCommand,
+		removeCommand,
 		setLabelCommand,
+		treeCommand,
 		unpackCommand,
+		usageCommand,
+		viewCommand,
 	},
 }