Remove testing support from the CLI

The testing support in the CLI has proven to be more trouble than
it's worth. Our recommendation is that, once an app gets to the stage
of requiring a test suite, it should be converted to a Maven or
Gradle project. This makes it easy to version, publish, deploy etc
using the vast ecosystems of the two build systems.

As part of this change, the dependency management for Spock has been
moved into spring-boot-parent, thereby making it "private". This
allows it to continue to manage the test-only Spock dependency in
spring-boot-test without also managing the version of Spring that is
used by a user's application.

Closes gh-9087
Fixes gh-9043

spring-boot-cli/src/it/java/org/springframework/boot/cli/CommandLineIT.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -45,7 +45,7 @@ public class CommandLineIT {
 		assertThat(cli.await(), equalTo(0));
 		assertThat("Unexpected error: \n" + cli.getErrorOutput(),
 				cli.getErrorOutput().length(), equalTo(0));
-		assertThat(cli.getStandardOutputLines().size(), equalTo(11));
+		assertThat(cli.getStandardOutputLines().size(), equalTo(10));
 	}
 
 	@Test