Use context class loader instead of one-off for command location

This works, and feels like the right thing to do, since there is no
guarantee that extensions won't in turn use ServiceLoader for things
that we haven't yet anticipated.

Fixes gh-6829. Cc @wilkinsona in case he has an opinion.

spring-boot-cli/src/main/java/org/springframework/boot/cli/SpringCli.java

@@ -31,6 +31,7 @@ import org.springframework.boot.cli.command.core.HintCommand;
 import org.springframework.boot.cli.command.core.VersionCommand;
 import org.springframework.boot.cli.command.shell.ShellCommand;
 import org.springframework.boot.loader.tools.LogbackInitializer;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.SystemPropertyUtils;
 
 /**
@@ -51,6 +52,7 @@ public final class SpringCli {
 		LogbackInitializer.initialize();
 
 		CommandRunner runner = new CommandRunner("spring");
+		ClassUtils.overrideThreadContextClassLoader(createExtendedClassLoader(runner));
 		runner.addCommand(new HelpCommand(runner));
 		addServiceLoaderCommands(runner);
 		runner.addCommand(new ShellCommand());
@@ -66,14 +68,14 @@ public final class SpringCli {
 	}
 
 	private static void addServiceLoaderCommands(CommandRunner runner) {
-		ServiceLoader<CommandFactory> factories = ServiceLoader.load(CommandFactory.class,
+		ServiceLoader<CommandFactory> factories = ServiceLoader
-				createCommandClassLoader(runner));
+				.load(CommandFactory.class);
 		for (CommandFactory factory : factories) {
 			runner.addCommands(factory.getCommands());
 		}
 	}
 
-	private static URLClassLoader createCommandClassLoader(CommandRunner runner) {
+	private static URLClassLoader createExtendedClassLoader(CommandRunner runner) {
 		return new URLClassLoader(getExtensionURLs(), runner.getClass().getClassLoader());
 	}